Double Chem Exam Flashcards

Question

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Answer 1

The type of attraction and the bond enthalpy (KJ/mol). Bond enthalpy means the energy required to break the bond or reaction. The first type of attraction we have in a water molecule is a covalent bond (O-H), the second type of bond we have is the hydrogen bond and the third we have is the instantaneous dipoles/instant dipoles. Instant dipoles are very short-lived.

Answer 2

a decent amount in So +464 KJ per mol. C-H bonds are a bit less than this at 300 KJ per mole, so these O-H bonds are pretty strong and need more energy.

Answer 3

The next type of bond we have is a hydrogen bond, much less energy needed about +10 to +40 KJ per mol. Much weaker but there are many of them that hold together a water molecule. For an instant, dipole it’s < +10. Instant dipoles are what make oil oily. It helps stick the chains together.

Answer 4

KJ mole-1 (said the same as kilojules per mole)

Answer 5

(between molecules). The strongest type of intermolecular force we can have is hydrogen bonding, then dipole to dipole and then van der Waals interactions. All these bonds affect the physical properties; they affect the melting point, the boiling point, they affect the solubility, and they affect the density.

Answer 6

kinetic energy of the particles in the system. So not all of the particles or water molecules will be at the exact same kinetic energy, so you can take the mean kinetic energy for them and use that value for the temperature. Therefore, T ∝ EK. EK = kinetic energy.

Answer 7

motion. Anything above absolute zero will have some kinetic energy. There are different types of kinetic energy; the first is translational energy or translation (movement from one place to another in a straight line), rotational energy or rotation (spinning about an axis), and vibration energy (so the atoms will move with respect to the central point or each other, bond stretching). Translation and rotation move on the X, Y, and Z axes.

Answer 8

Water molecules have hydrogen bonding, Iron has metallic bonding. Hydrogen bonding, so it heats up slowly. Metallic bonding heats up quickly. Puddle is not hot to the touch, but the iron is very hot to the touch. In water, we can break the hydrogen bonds before the water increases in kinetic energy. H bonds are broken before the water molecules can increase their energy (a very slow process). With metal cations are fixed in place, it’s the electrons that are moving. So they vibrate faster straight away, which is fast (more kinetic energy increase), therefore higher temperature. Metallic bonding is incredibly strong, takes even more energy to break than a covalent bond.

Answer 9

a homogeneous mixture composed of two or more substances. One of which will be the solute, and one of which will be the solvent. Solute: the minor component (can be a solid, liquid or gas) dissolved in a solvent. Solvent: able to dissolve other substances.

Answer 10

like. For a polar solvent, you’ll need a polar solute. For a nonpolar solvent, you’ll need a nonpolar solute. A mixture of both polar and nonpolar substances to dissolve something that isn’t very polar or nonpolar.

Answer 11

Homogeneous mixture (sugar + water = solution) or heterogenous mixture (sand + water = no solution) A homogeneous mixture creates a solution.

Answer 12

suspension (solute particles don’t dissolve, but are suspended through the bulk of the solvent, like flour and water), it can be an emulsion (it’s the mixture of two liquids, but one liquid is dispersed in another, like milk with fats in water), and collids (intermediate case, heterogenous but solute particles are smaller).

Answer 13

Sodium chloride (table salt), an ionic solution, will dissolve in water, forming an aqueous solution. So ionic molecules will dissolve in water to form what’s called an aqueous solution. The ionic bond is broken, and the molecule dissociates (breaks down) into its ions, and these ions are surrounded by the water molecules. The reason this happens is because the water is polar.

Answer 14

central metal ion, often a transition metal, is bonded to one or more molecules or ions. For Na forms a complex ion. A complex ion has the metal at its centre. It has the metal cation at the center, it will have one or more ligands (something attached to a metal) attached via a dative covalent bond. The ligand here is the water, attached to the sodium ion. A dative covalent bond is where both of the electrons bond/come from the same atom (normal covalent bonds have shared electrons). In this case, it’s the oxygen atom. Formula for the reaction is: NaCl(S) + H2O(L) → Na+(aq) + Cl-(aq) It’s still surrounded by the water, but it’s not creating a complex ion. The aq denotes that it’s aqueous, so surrounded by water. The reaction shows that the sodium chloride has diassociated into that cation and anion which have now been surrounded by the water.

Answer 15

dissolving. There is only a finite amount of water molecules to surround the molecules. So in this case, the sodium chloride wouldn’t disassociate any more and would stay the same. The number of water molecules to dissolve/surround an ion depends on the ion, but for sodium, it needs 6 water molecules per sodium molecule. At the saturation point, the concentration of the solution will not increase, as no more ions are being dissolved into it. At this point, the solution has reached equilibrium.

Answer 16

ess solute and therefore are capable of dissolving solutes. Solutions can be saturated, which means no more solute can be dissolved. We also have super saturated, which means we have more solute than can be dissolved, which creates a precipitate. Precipitation means a solid forming out of the solution, cations and anions in an aqueous solution, combine to create an insoluble ionic solid (called a precipitate). It could be insoluble due to there not being enough water molecules to surround it or there could be other reasons.

Answer 17

- Ionic compounds are generally soluble in water (aqueous systems), but there are exceptions - Need to learn what will and what will not be soluble Note: Calcium hydroxide is only slightly soluble in water, you need to heat it up to get it to dissolve. Examples: KBr is soluble AgCl is insoluble MgCo3 is insoluble. If we want to predict precipitation, we need to know what you’re starting with and how they will behave in solution (soluble or insoluble according to the rules/table).

Answer 18

1) Know the formula/formulae of the starting solutions. 2) Know the cations (metal, what charge) and anions (nonmetal, what charge) in solution 3) Work out the new salts formed 4) Decide if the salts formed are soluble or insoluble. If insoluble, a precipitate is formed.

Answer 19

Some reactions go to completion, with reactant conversion to a product. Virtually all the reactants are converted into products. This is represented by a single arrow pointing to the product (→). Example: AgNO3(aq) + NaCl(aq) → AgCl(s) + NaNO3(aq)

Answer 20

equilibrium. Represented with ⇌. Both reactants and products are present, so we have a state of balance. No net change in the amount of reactant and product.

Answer 21

At equilibrium, the rates of the forward and reverse reactions are equal. It looks like nothing is happening/nothing appears to happen. It’s important to realise it is happening, a forward and reverse reactions are occurring, called dynamic equilibrium (⇌).

Answer 22

- The concentration of reactants (in the solution) - Pressures of the reacting gases - Temperature

Answer 23

When an external charge is made to a system, and that system is in dynamic equilibrium. When you make a change to the dynamic equilibrium, the system responds to minimise the effect of the change.

Answer 24

There are two examples: one where a change can be enforced by changing pressure, and one where a change cannot be enforced by changing pressure. a) Reaction of nitrogen and hydrogen gas to form ammonia gas. It’s the Haber-Bosh process. N2(g) + 3H2(g) ⇌ 2NH3(g) Left side: 4 molecules, 1x N2 and 3x H2 Right side: 2x NH3 An increase in pressure moves the position of the equilibrium to the side with the fewest gas molecules, what this does is reduces the pressure. The system is minimising the effect of change. The Haber-Bosh process is carried out under very high pressure. b) Reaction og hydrogen with iodine gas to form hydrogen iodide. H2(g) + I2(g) ⇌ 2HI(g) Left side: 2 molecules, 1x H2 and 1x I2 Right side: 2 molecules, 2x HI The change in pressure will not have an effect on the position of equilibrium. Change in temperature: Nitrogen dioxide (dioxide = 2 oxygen) is in equilibrium with its dimer (2 things stuck together), dinitrogen tetroxide (tetroxide = 4 oxygen). NO2(g) ⇌ N2O4(g) Nitrogen dioxide is brown, dinitrogen tetroxide is colourless. Forward reaction is exothermic (heat given out) The reverse reaction is endothermic (heat taken in) If we place a sealed vial in boiling water > it becomes dark brown If we place a sealed vial in ice water > it’s almost colourless. Change is based on the temperature. As the temperature increases, the equilibrium position is moved by the system into the endothermic position to lower the temperature. As the temperature decreases, the equilibrium position is moved by the system into the exothermic position to increase the temperature.

Answer 25

Concentration: ↑ reactant concentration, pushing the formation of the product. ↑ product concentration, pushing the formation of the reactant. Pressure: ↑ pressure, favours the side with fewer molecules ↓ pressure, favours the side with more molecules Temperature: ↑ temperature, favours the endothermic reaction ↓ temperature, favours the exothermic reaction

Answer 26

Symbol is Kc. At equilibrium, the concentrations of the reactant and the product are related. aA + bB ⇌ cC + dD Lowercase a,b,c, and d are stoichiometric coefficients or the amount of reactants and products. Uppercase A,B,C and D are the reactants and products themselves. [A], [B], [C], and [D] represent the concentrations of A, B, C and D. Kc = equilibrium constant for concentration (what we want to work out) The numerator is the concentration of products raised to the power of the coefficient. The denominator is the concentration of reactants raised to the power of the coefficient. This equation is used for gases and solutions (not solids or liquids).

Answer 27

temperature

Answer 28

- The value of Kc does not vary when different amounts of concentration are used or when pressure is altered, because it’s a ratio. - The value of Kc does vary with temperature. Always state the temperature value with the Kc

Answer 29

Units will vary depending on the reaction.

Answer 30

For equilibrium expression, it only includes substances that are in gaseous or aqueous states, so not solids or liquids. This does not make sense to discuss solid or liquid in terms of concentration, they cannot change like it can in gases and solutions.

Answer 31

It measures the relative amounts of products and reactants present during a reaction at a particular time. It could be at equilibrium, or it may not be at equilibrium. We can use this to predict the direction the reaction from that point in time. We can do this because the amount of product and reactant will cange until equilibrium is reached. We need an expression for the reaction quotient, which is Q

Answer 32

The reaction will make more product to reach equilibrium.

Answer 33

The reaction will make more reactant to reach equilibrium.

Answer 34

The reaction is already at equilibrium.

Answer 35

When a reaction goes to completion (A + B → C), it is easier to work out the amount of product formed. We need to do some maths to calculate concentrations at equilibrium.

Answer 36

Very general definition. For an acid, they have a sour taste, are corrosive, they’ll turn blue litmus paper red, and they’ll have a pH of less than 7 @ 25oC. For a base, they have a bitter taste, they can be corrosive, they’ll turn red litmus paper blue and they’ll have a pH of more than 7 @ 25oC.

Answer 37

alkalis. All Alkalis are bases, but not all bases are alkalis (as not all bases are soluble).

Answer 38

1) Arrhenius theory: This only applies to aqueous solutions. An acid is something that will give you hydrogen ions (H+) or protons in a solution; the concentration of the ions increases. Substances that will give hydrogen ions/protons. A hydrogen has 1 proton in the nucleus and 1 electron; if that electron is lost, there is just one proton, hence why they are known as hydrogen protons. In a solution (must be aqueous), the concentration of H+ is increased. 2) Brønsted-Lowry theory: Acids are hydrogen ion/proton donors. When you do something with them, they donate a proton. Bases are hydrogen ion/proton acceptors. When you do something with them, they accept a proton. 3) Lewis theory This gets rid of the whole association with elements and deals with whether something is an electron acceptor or an electron donor. Acids are electron acceptors and bases are electron donors.

Answer 39

Acids and bases have conjugate bases and conjugate acids. They are the product form in acid/base reactions. A conjugate acid and a conjugate base form a conjugate pair. Acid + Base ⇌ Conjugate Base + Conjugate Acid Acid is the proton donor, Base is the proton acceptor. Conjugate Base is Acid minus H+, Conjugate Acid is Base plus H+.

Answer 40

amphiprotic, so water can be amphiprotic.

Answer 41

An acid and a base react to give a salt and water. It includes the combination of H+ and OH- to generate water.

Answer 42

A strong acid or base is nearly or completely ionised (forming ions) in water. Conductivity is high. A weak acid or base is only partially ionised (forming ions) in water. Conductivity is low.

Answer 43

acidity constant or acid dissociation constant. An expression for how much dissociation has taken place. Generally applicable to weak acids only, if a strong acid that fully dissociates wouldn’t need this used.

Answer 44

basicity constant or base dissociation constant. An expression for how much dissociation has taken place. Generally applicable to weak bases only, if a strong base that fully dissociates wouldn’t need this used.

Answer 45

ions, the reaction goes to completion. 1 mol HCl will form 1 mol of H3O+ ions in solution. Not in equilibrium, so no equilibrium constant. The equations are otherwise the same as the previous equilibrium equations.

Answer 46

pH level, the concentration gives a good idea in the ballpark of what the pH of a solution will be.

Answer 47

if it makes sense in the context of what you’re calculating.

Answer 48

This describes the acidity of a particular molecule. pKa: pOH = -log10 Ka (pKb: -log10 Kb) The concentration amount (moles) of substance per 1 L, the strength is about the degree of ionisation.

Answer 49

strong acid

Answer 50

The process of adding a substance with a known concentration (titrant) to a substance with an unknown concentration (analyte) to determine its concentration. pH of the solution changes when the acid and base are reacted.

Answer 51

pH increases.

Answer 52

pH decreases.

Answer 53

Chemically equivalent quantities of base and acid that have been mixed. The number of moles of acid will match the number of moles in the base (the numbers are equal).

Answer 54

Is the point where the indicator changes colour. Gives us an estimation of the equivalence point/a rough idea where the equivalence point is. But it won’t be the exact place. Indicator: Is a weak acid or a weak base; it will be in some sort of equilibrium. Where the conjugate has a different colour to this weak acid or base. Indicators state pH range of colour change on the bottle.

Answer 55

In weak acid/strong base titration, the pH initially rises (6), then levels off (7). This is called the buffer region. A buffer is a mixture of a weak acid and its conjugate base. If you have a small amount of acid (H+/H2O+) added, then the base component neutralises it. This prevents a drop in pH. Likewise, if you have a small amount of base added (OH-), then an acid component neutralises it. This prevents an increase in pH. pH + pOH = 14

Answer 56

Greek: Thermo - heat, Dynamikos - force or power This is the study of the relationship between heat, work, temperature and energy. The laws of thermodynamics describe how the energy in a system changes and whether the system can perform useful work on its surroundings. (system and surroundings are key in thermodynamics) Changes can be chemical (like rust forming) or phase changes (like when ice melts).

Answer 57

change occurs. E.g. rust forming is very slow, while ice melting is reasonably fast.

Answer 58

observation.

Answer 59

The capacity to do work or to produce heat. For example, steam pushing a piston (work) or steam heating something (producing heat).

Answer 60

Moving things around (like molecules). Depends on pressure and volume.

Answer 61

The thermal energy transferred between two systems at different temperatures that come into contact. If they’re at the same temperature, there will be no thermal transfer of energy, therefore no heat.

Answer 62

The absolute measure of the average total internal energy of an object. So it’s a number of the total internal energy of an object. Total internal energy is called the kinetic energy/how much stuff is moving around.

Answer 63

interchangeable, these two things are not the same.

Answer 64

Heat: Amount of energy in an object. Heat depends on the amount of material. Temperature Intensity of the heat. Temperature does not depend on the amount of material.

Answer 65

same. Absolute temperature needs to be converted to K, so add 273 on. Temperature change (ΔT) does not need to be converted to K. System and Surroundings: It’s important to define these for calculations.

Answer 66

Object(s) being studied, the thing of interest.

Answer 67

Everything outside the system that can exchange energy with the system.

Answer 68

system boundary (so a beaker or conical flask). We have to identify the system and it depends on the circumstance. E.g. Heat evolved/generated in a chemical reaction. The system would be the reaction vessel and content, the surroundings would be the air, the bench, clamp base, etc.

Answer 69

temperatures. We usually go from hot to cold. The symbol for heat is q. Units are J or KJ.

Answer 70

Exothermic and Endothermic

Answer 71

Heat transferred from the system to the surroundings. Heat given out. Freezing water, releasing heat, so is exothermic.

Answer 72

Heat transferred from the surroundings to the system. Heat taken in. Melting ice, heat is absorbed, so is endothermic.

Answer 73

Conversion of energy. Energy can be converted from one form to another, but it cannot be created or destroyed. Example: ice melting in your hand. Ice feels cold because the heat (thermal energy) from your hand is transferred to it, you are losing energy by melting that ice. Ice gains energy, which is used to break the H bonds holding the molecules of water together. The same total amount of energy still exists, the energy has just been transferred. Relates to heat capacity.

Answer 74

Heating causes a change in temperature (T). Different substances heated with the same amount of energy do not give the same temperature changes (∆T). Heat capacity (c) quantifies the energy change. This is the heat needed to raise the temperature of a substance by 1 K (Kelvin).

Answer 75

This refers to 1g of substance. For example, water has high cs, so we need lots of energy to increase its temperature. Metals have a low c, so less energy is required to increase their temperature. Think about the bonds of these.

Answer 76

hotter/the final temperature will be higher due to its low specific heat capacity (cs).

Answer 77

Delta. Delta just means change, the final - initial. If the temperature gets colder, the ∆T and q will be negative. This also hints at an exothermic or endothermic process taking place.

Answer 78

lower than the initial temperature. Making ∆T negative, therefore q is negative, making it an exothermic process.

Answer 79

higher than the initial temperature. Making ∆T positive, therefore q is positive, making it an endothermic process.

Answer 80

Solid melting - Atoms/molecules do move, but in place. Melting breaks the attractive forces. Liquid boiling - Atoms/molecules move far apart. Boiling makes the attractive forces minimal. These are called phase changes.

Answer 81

We need energy to overcome the attractive forces. During changes of state, energy (heat) is absorbed, but temperature remains constant. In the reverse process, the same amount of energy (heat) is released.

Answer 82

Heat of fusion - the energy required to melt a solid into a liquid. Heat of vaporisation - the energy required to vaporise a liquid into a gas. Heat of sublimation - energy required to sublime a solid to a gas. All units are Jg-1 (Joles per gram).

Answer 83

Has a specific definition all to do with the energy of the system. Enthalpy is the sum of a thermodynamic system’s energy and the product of its pressure and volume. Symbol is H. H = E + P x V H = Enthalpy, E = Internal energy (u), P = Pressure, V = Volume. Enthalpy is a state function (it measures where you are at this point, not the route it takes to get there). Enthalpy change ∆H is the change in enthalpy during a process - final - initial.

Answer 84

state function - it measures where you are, not the route to get there.

Answer 85

enthalpy during a process - final - initial.

Answer 86

enthalpy in the reaction as written.

Answer 87

∆rH < 0. The enthalpy decreases, and the heat is transferred from the system to the surroundings. Gives out heat.

Answer 88

∆rH > 0. The enthalpy increases, and the heat is transferred from the surroundings to the system. Takes in heat.

Answer 89

endothermic Occurs during chemical reactions.

Answer 90

exothermic Occurs during chemical reactions.

Answer 91

Depends on the amount of matter in the sample. Examples of these properties include mass, volume, entropy (order of a system/how ordered it is) and enthalpy.

Answer 92

Does not depend on the amount of matter in the sample. Examples of these properties include temperature, density, and hardness.

Answer 93

This law states that the total enthalpy change for a chemical reaction is independent of the path by which the reaction occurs. It depends only on the initial and final states. If a reaction is the sum of two or more other reactions, then the ∆rHo (change in standard enthalpy) is the the sum of each indidival ∆rHo.

Answer 94

symbol is o, ∆rHo.

Answer 95

1 mol/L or 1 mol L-1

Answer 96

no standard T, should always be stated. Values usually given at 25oC or 298K.

Answer 97

Solutions get hotter or colder depending on the salt added (remember any ionic compound can be considered a salt). Think in terms of Hess’ Law.

Answer 98

Enthalpy of formation of 1 mole of solid salt from ions in the gas phase. Negative and large (exothermic).

Answer 99

The amount of heat released when 1 mole of the ion dissolves in a large amount of water, forming a solution. Negative and large (exothermic). Also has ionic-dipole interactions.

Answer 100

Amount of heat that is released or absorbed during dissolving at a constant pressure. Can be positive or negative (exothermic or endothermic).

Answer 101

∆FHo Ethalpy change of 298.15 for the formation of 1 mole of compound directly from its component elements in their standard state. Standard state: Most stable form at 298.15K and 1 bar pressure. It’s not the same as the natural state of the element. ∆FHo for an element in its standard state is zero (0). We cannot make an element from something else, element are the building blocks. O2(g), Cl2(g), Cu(s), Ar(g)

Answer 102

It’s whether a reaction occurs based on the thermodynamics and the kinetics. A reaction that can occur from the thermodynamic consideration is called spontaneous. For example ice melting at 10oC or conversion of diamond to graphite. Spontanouies does not mean fast, it can be slow reactions.

Answer 103

Thermodynamically cannot occur under the given conditions. For example forming ice from water at 10oC. Exothermic reactions are not always spontaneous. For example stream condensing to water, but can only occur under certain thermodynamic conditions like the te,peratour being below 100oC. Endothermic reactions are not always non-spontaneous.

Answer 104

1) Spontaneous at all T (except for 0 Kelvin). 2) Spontaneous or nonspontaneous depending on what T.

Answer 105

1) Non-spontaneous at all T (including 0 Kelvin). 2) Spontaneous or nonspontaneous depending on what T.

Answer 106

∆H - Enthalpy T - Temperature S - Entropy

Answer 107

Symbol is S. Entropy is the amount of order or disorder in a system. Things tend to become more disorded - Entropy increases. ∆S is positive. Entropy is a state function units: JK-1mol-1, J/K/mol Entrophy for pure substances. Standard entropy, 5o298 S increases from solid → liquid → gas Increasing disorder.

Answer 108

entropy of the universe.

Answer 109

∆Stotal = ∆Ssystem + ∆Ssurroundings

Answer 110

∆rH is negative because when heat is added to the surroundings, entropy increases (positive) and ∆rH is negative. Multiply by -T. => -T ∆Stotal = ∆rH - T∆Ssystem ∆g = ∆H - T∆S. ∆g = Change in gibbs energy of system. ∆H = Change in enthalpy of system. T = In Kelvin. ∆S = Change in entropy of system. If… ∆g < 0 (negative) - spontaneous reaction ∆g > 0 (positive) - non-spontaneous reaction ∆g = 0 - reaction is at equilibrium

Answer 111

In a chemical reaction, the reactants ‘collide’ with each other For a reaction to occur, some conditions must be met, reactants must collide with: 1. The right orientation 2. Enough energy These conditions are required for the positions of electrons to change in the forming and breaking of chemical bonds between atoms.

Answer 112

A principle used to help predict the rates of chemical reactions

Answer 113

Reactions rates are how fast a chemical reaction occurs. Chemical kinetics is the study of reaction rates. * How rates of chemical reactions are measured and predicted. By contrast, thermodynamics tells us whether a reaction can occur (is spontaneous) or cannot occur (is non-spontaneous). Thermodynamics tells us nothing about how fast spontaneous reactions occur. Kinetics here is a synonym with rates of reaction; compare to physics where kinetics is about the motion of objects due to kinetic energy

Answer 114

* Degradation rates of food, pharmaceuticals, other consumer products, plastics, metal structures (corrosion), etc. * Ripening rate of fruit. * Weathering of stone/rock by wind and water. * The effects of pollutants on the environment, etc. All these macro-effects are ultimately driven by the rates of underlying chemical reactions.

Answer 115

Most reactions don’t just go A + B = C. There are usually intermediates and multiple steps involved. Reaction mechanisims are the sequence of steps that give the overall reaction. A reaction involving more than two species (atoms, molecules, or ions) is highly unlikely to occur in a single step. It is unlikely that more than two components will collide in the right orientation with the right energy (etc.) simultaneously and allow the reaction to proceed in a single step. Even a reaction between two species may not occur in a single step…

Answer 116

* Understanding and treatment of disease * Optimising industrial processes * Understanding reactions in the atmosphere (ozone hole, climate change), etc.

Answer 117

reaction mechanisms.

Answer 118

Reaction mechanisms are the sequence of elementary steps by which the overall reaction occurs (elementary step = single step).

Answer 119

A chemical equation that describes a single molecular event, such as the formation or rupture of a chemical bond

Answer 120

the number of molecules reacting in an elementary step.

Answer 121

one molecule.

Answer 122

two reactant molecules colliding.

Answer 123

three reacting molecules colliding (rare).

Answer 124

The time it takes to complete all the steps (i.e. the reaction mechanism) defines the overall reaction rate. In a multi-step (two or more steps) reaction, the slowest step is the rate-determining step. It controls the overall reaction rate.

Answer 125

Consider how the amount of the reactants or products change over time. e.g. analogous to the speed of a car. Reactants → products If the reactants and products are present in the same solution, the molar amounts can be replaced by concentrations. Time is typically in seconds.

Answer 126

The overall rate of a reaction is always positive. Think of the car analogy, can’t have a negative speed of a car.

Answer 127

lowered. The disappearance of a reactant = [R]final - [R]initial will always be negative. The relative rate of a reactant is always stated as minus.

Answer 128

concentration. E.g. the concentration of NH3 we can write as [NH3].

Answer 129

If you know the overall rate for a reaction, you can calculate the relative rate for each component.

Answer 130

“change” By convention positive rates are stated for products, negative rates stated for reactants

Answer 131

Remember collision theory. Reactants usually must collide to react. The higher their concentration, the more successful collisions (i.e. correct energy and orientation of reactants) and the greater the reaction rate. The rates of most reactions depend on the concentration of reactions. This relationship can be stated mathematically. These are called rate laws or rate reactions. Rate equations (rate laws) give the relationship between the concentrations of reactants and the rate of reaction Rate laws are mathematical expressions that link the rate of a reaction to the concentration of each reactant.

Answer 132

[A] and [B] are the concentration of each reactant. k is the rate constant (rate coefficient). * A larger value means a faster reaction. * k depends on temperature, so is calculated for a particular temperature. m and n are “orders”, their values are not necessarily equal to a and b. This assumes the reaction goes to completion (no reverse reaction), or that only the initial rate is analysed (so the initial product concentrations are almost zero).

Answer 133

The exponent powers m and n give the ‘order’ with respect to that reactant, called “partial orders of reaction”. The sum of the partial orders is the overall order of reaction. Orders quantify the degree to which the rate of a chemical reaction depends on the concentration of each reactant, as well as which species has the greatest effect. aA + bB xX + yY Rate = k[A]m[B]n 1: 1st order (remember, no power = 1) 2: 2nd order 3: 3rd order Etc. 0: zero (or zeroth) order, means a reactant doesn’t appear in the rate law (any number to the power 0 = 1, e.g. [A]0 = 1.

Answer 134

The partial orders of a reaction depend on the reaction mechanisim. * Determining partial orders can help identify the mechanism. Also allow us to understand the rate law, units of the rate constant, half-life of reactants.

Answer 135

* If zero, the concentration of that reactant does not affect the rate (and the term will not appear in the rate law). * Negative: concentration inversely affects the rate (rare). * Positive integer: directly affects the rate (positively). * Fractional: both positive and negative, intricate relationship between concentration and reactant and rate, more complex reactions.

Answer 136

aA + bB xX + yY Rate = k[A]m[B]n k is the rate constant (rate coefficient) * A larger value means a faster reaction * k depends on temperature, so is calculated for a particular temperature What are the units of the rate? mol L-1 s-1 The units of k depend on the total order of reaction

Answer 137

‘collide’ with each other. For a reaction to occur, some conditions must be met, reactants must collide with: 1. the right orientation 2. enough energy

Answer 138

B = C. There are usually intermediates and multiple steps involved (a reaction mechanism).

Answer 139

fast chemical reactions occur - depends on the slowest step. Rate laws are mathematical expressions that link the rate of a reaction to the concentration of each reactant. aA + bB xX + yY Rate = k[A]m[B]n

Answer 140

of a chemical reaction depends on the concentration of each reactant.

Answer 141

n of each reactant. k is the rate constant (rate coefficient) and a larger value means a faster reaction. The units of the rate are mol L-1 s-1, and the order of reaction affects the units of the rate constant

Answer 142

Strategy: 1. Choose two experiments where one reactant concentration is the same, and the other varies. 2. Write out the rate expressions (easier if the higher rate is on top). 3. Solve for the partial order. 4. Repeat for other reactant(s) Use experimental data to derive the rate law Rate = k[A]m[B]n

Answer 143

rates of reactions usually change with time. The concentration of reactants decreases throughout the reaction, and therefore the rate is also decreasing (k, however, remains constant). Rate of reaction usually decreases with time

Answer 144

start of the reaction when the concentrations are known (initial rate). Rate = k[A]m[B]n Integrated rate equations to determine equation params

Answer 145

experiments to calculate the rate constant, k, , and reaction order(s). These give the rate law and so the reaction rate can be calculated for any set of reactant concentrations. To determine the rate constant, k, and reaction order(s), we use integrated rate equations.

Answer 146

integrated rate equations. It’s easier to determine the rate constant, k, and reaction order using these equations, rather than using the actual rate laws. You only need to know how to use the equations, not how to derive them. Example: First-order reaction Reactant(s) (R) → Products For the first-order rate equation: Rate = k[R] Integrated rate equation: In([R]t/[R]0) = -kt Where: [R]t is concentration of R, at time t [R]0 is concentration of R, at time t = 0 (i.e. initial [R]) If you know the initial concentration, [R]0, and the concentration at time t, [R]t, you can calculate k. Once you know k, and knowing the initial concentration, [R]0, you can calculate [R]t, which is how much R will be there at any time t. This is often useful or important to know.

Answer 147

ln[R] vs t gives a straight line with a slope of –k. Zero and second order integrated rate laws Straight lines are expected for the integrated rate laws for other reaction orders

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Usually, the most reliable method for determining the order of a reaction and the rate constant is to: * Collect [R]t vs t data * Plot the data different ways, based on the integrated rate equations. One plot will be linear, and others will be curved. The linear plot matches the correct rate law (i.e. gives order). From slope, get k (or –k, depending on the rate law). Is this reaction fast or slow; will it take seconds, hours, or days to fully decompose azomethane? Calculating the half-life, t1/2, gives this information. Half-life of first-order reactions The half-life is the time required for the concentration of a reactant to halve. Half-life of first-order reactions The half-life is the time required for the concentration of a reactant to halve. t1/2 does not depend on the concentration of reactant, only the rate constant. Regardless of the [reactant], for a first order reaction, after a time period of 0.693 / k, the [reactant] will have halved. If the time taken for the concentration to halve is known, k can be calculated.

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Rate = k[A]m[B]n Rate depends on [reactants] (except for a zero-order reaction). Rate depends on k. k depends on temperature (T). For most reactions, k increases as the temperature increases, and so the reaction occurs more rapidly.

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For a reaction to occur: Reactants must collide with the correct orientation and with sufficient energy to initiate bond breaking and forming. This energy is the activation energy, Ea. The reaction rate depends on: * The frequency of collisions between reactants. * The frequency of collisions with correct orientation. * The number of molecules (and collisions) with energy >= activation energy. All of these increase with temperature. The biggest effect on reaction rate as temperature increases is the increased number of molecules/collisions with energy ≥ activation energy.

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energies In a gas, the average kinetic energy of molecules or atoms is constant at constant temperature, but there is a range of kinetic energies. Catalysts increase the rates of reactions A catalyst increases the rate of a reaction by giving a different reaction pathway, which has a lower activation energy. Catalysts are not consumed in a reaction; usually only a small amount is needed. Enzymes catalyse biological reactions.

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Redox reactions are a class of chemical reactions where the oxidation states of components change. This can be: * Oxidation – the loss of electrons/increase in oxidation state * Reduction – the gain of electrons/decrease in oxidation state These processes are intrinsically linked - for one to occur so must the other.

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Oxidation is loss, reduction is gain (of electrons)

Answer 154

Reduction and oxidation Remember – all redox reactions involve both reduction and oxidation processes, they go hand- in-hand

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gain or loss of electrons Refer back to the experiment of various metals in metal solutions. There was no oxygen involved in these reactions. What changed? The number of electrons on the metal changed/charge on the metal changed. Redox can be defined in terms of gain or loss of electrons.

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loss of electrons is oxidation, gain of electrons is reduction. This can also be expanded to LEO’s A GERC – loss of electrons is oxidation (at the anode), gain of electrons is reduction (at the cathode).

Answer 157

Oxidation states and numbers are useful Not all cases are as easy to see as the ones so far. e.g. for uncharged molecules, or for polyatomic ions, oxidation numbers/oxidation states are used. Oxidation numbers are the hypothetical charges that would be present on an atom if the electrons in all bonds were transferred (i.e. if all bonds were fully ionic). This does not mean that they were transferred, and it does not represent the “real” charge on that atom – it is a tool to work out transfer of electrons (redox) in compounds.

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its oxidation number increases.

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its oxidation number decreases.

Answer 160

1) The oxidation number of each atom is a pure element is zero. 2) The oxidation number of an atom in a monoatomic ion is the charge on the ion 3) The oxidation number of each oxygen atom in all compounds of oxygen (except peroxides and superoxides and F2O) is -2. Peroxides : R-O-O-R/Superoxide: O2- 4) The oxidation number of each hydrogen atom in all compounds of hydrogen (except metal hydrides) is +1. In metal hydrides, it is -1. 5) The total oxidation number of the atoms in an uncharged molecule is zero. 6) The total oxidation number of the atoms in a polyatopmic ion is the charge of the ion.

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reductant. Oxidant = oxidising agent (itself is reduced) Reductant = reducing agent (itself is oxidised). Criteria for reduction: Loss of oxygen Gain of electrons (RIG) Decrease in o.n. Gain of hydrogen

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Loss of electrons, more positive, reducing agents

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Gain of electrons, more negative, oxidizing agents

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metals. * Mostly have one or two valence electrons * All have low electronegativity * Achieve stable outer arrangement by donating their outer valence electrons to an oxidant * In the case of metals – will be oxidised to its ion * The metal ion is the conjugate oxidant to the metal Are oxidised, loss of electrons, more positive

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non-metals * Non-metals with high electronegativity need electrons to complete their valence shell * Will accept electrons from sufficiently strong reductants * Form negatively charged ions Are reduced, gain of electrons, more negative Some species can act as both an oxidant or a reductant

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eduction and oxidation. Each of these processes can be represented as a separate half- reaction.

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K: balance the key element O: balance any oxygen loss or gain by adding H2O to the appropriate side H: balance hydrogen by adding H+ ion(s) to the appropriate side E: balance the total charge by adding electrons to the appropriate side S: add the appropriate states (phases) to each reaction component in the final, balanced equation

Answer 168

It is assumed the reactions are in acidic conditions; therefore, it is valid to balance using H+.

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Balance the half equations as previously (as though it is acidic conditions). * Add OH- to neutralise H+ ions on either side of the equation. * Form water by combining H+ and OH-. * Combine the half reactions and check that the elements and charges are balanced. Multiply the oxidation reaction by 2 and the reduction reaction by 3 to balance the electron counts (cancelling them out).

Answer 170

redox reaction Most metals are found in their oxidised form as oxides. Corrosion of iron (only) is called rusting. Corrosion is the metals going back to their original form (oxidised). Solutions to undesirable oxidation Use a sacrificial metal, such as, zinc. Other ways of dealing with rust/corrosion Painting Non-oxidising layer (aluminium does this by itself) Electroplating – e.g. chromium, silver Galvanising – zinc coating Coating in oil (hydrophobic layer) Galvanising A protective zinc coating applied to iron or steel to prevent rusting. The most common method is hot-dip galvanising, i.e. submerging the iron/steel in a bath of molten zinc. Galvanizing protects in two ways: * Coating of corrosion-resistant zinc (zinc carbonate) which prevents corrosive substances from reaching the steel/iron beneath. * The zinc also serves as a sacrificial metal, so that even if the coating is penetrated/compromised, the zinc is oxidised in place of the iron/steel.

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Organic chemistry is the study of molecules containing carbon. These molecules are all around us: Estimate of ~20,000,000 organic compounds are known – billions possible – being discovered constantly. Your body is already an adept organic chemist! Just moving around your body does organic chemistry – reactions in your muscles turn sugar and oxygen into energy

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humans and lasts generally no more than about 60 s. We turn over 50-70 kg of it per day. As you understand this, your brain cells are being bridged by organic molecules, passing nerve impulses around your brain Many roles, including with memory, attention, and learning. Involved in controlling mood (and many other things!). To make our minds as good at organic chemistry as our bodies we need to build a good understanding of the basics!

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synthesised. Organic chemists synthesise molecules containing carbon and look at their properties. Here is a laboratory preparation you have done Organic compounds are prepared by chemical synthesis Naturally-occurring compounds of astonishing complexity have been prepared in the laboratory by synthetic organic chemists

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four atoms. The bonds are covalent– electrons shared between atoms. Compare to: Nitrogen: 3 bonds. Oxygen: 2 bonds. Fluorine: 1 bond. … allows structural diversity – many millions of organic compounds!

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Stability: carbon forms strong bonds to other carbon atoms. E.g. in diamond: Oxidation of carbon is slow… (need high temperature to start)

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Recall prior lectures… Carbon likes to bond to four atoms (has four valence electrons). The bonds will be covalent – electrons shared between atoms. From Valence Shell Electron Pair Repulsion (VSEPR), carbon will have a tetrahedral geometry.

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hydrocarbons.

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Yes! When this happens, the compound is called an alkene. Each carbon still forms four bonds.

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Yes! These are e.g. dienes and trienes.

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Yes! These are alkynes.

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Line-bond drawings show the carbon skeleton. Other atoms are represented with their elemental symbol. Drawn like a zig-zag, carbon atoms are at the end of each straight line. There is a carbon at each end and each bend! Double bonds are shown as two parallel lines and triple bonds are three parallel lines. Note that we leave the hydrogen atoms off. We know that carbon always forms four bonds, so any spare bonds will be connected to hydrogen. We leave the hydrogens on atoms other than carbon. Here is the structure of ethanol.

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isomers These are structures with the same formula, but different ways of being put together.

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hydrogen only. They are called hydrocarbons.

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carbon-carbon bonds.

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carbon-carbon bonds.

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carbon-carbon bonds.

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Naming organic structures is easy – you just follow simple rules and practice, practice, practice!

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finding the main chain The length of the chain tells us what the rest of the name will be Number the longest carbon chain, use that as the name of the compound.

Answer 189

Many compounds have more than one chain. These are referred to as substituents. Number the longest chain, use that as the principal name of the compound.

Answer 190

The extra branches, or substituents, on the chain are identified by their name and point of attachment. We identify the point of attachment by using the number of that carbon in the chain. Point of attachment is at carbon 3 of the parent chain. The name of the hydrocarbon substituent (alkyl group) is derived from the number of carbons it has (similarly to the parent).

Answer 191

Substituents are atoms or groups of atoms that replace hydrogen and get attached to the carbon in the longest carbon chain. Substituents are referred as alkyl groups. = alkanes missing one hydrogen.

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Step 1 Find the longest carbon chain. Step 2 Number the carbon chain so you have the most substituents and lowest number at each substituent. Step 3 Identify the type of substituent. Naming alkanes with two of the same substituents Number,number-prefix substituent longest carbon chain What if there is more than one chain? There can be more than one alkyl substituent on a compound. If those are the same, we use the prefix (2), (3), etc. Again, we start by numbering the longest chain. This time there are two different ways, we use the one that will get to the substituents the soonest. Naming alkanes with two different substituents Number-substituent-number-substituent longest carbon chain. Always write substituents in alphabetical order

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name. The first functional groups we saw were alkenes and alkynes. We use the suffixes –ene and –yne for these We still have to count the carbons to determine the name of the parent chain. We then replace –ane with the correct suffix. Names of alkenes are similar to alkanes The bigger the alkene, the trickier the name …

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(A) Parent chain is pentane. Double bond is between C1 and C2. Pent -1-ene. (B) Parent chain is pentane. Double bond between C2 and C3. Pent -2-ene.

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carbon-carbon bonds of different nature.

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longest carbon chain, and the primary type of hydrocarbon they can be identified as.

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Alcohols, ethers, aldehydes, ketones, and carboxylic acids.

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Carbon can form bonds with other atoms. The properties of the new compound will be different. A functional group is a specific type of substituent attached to the carbon chain.

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groups. Because they have different reactivity to alkanes, double and triple bonds are considered functional groups. Double bonds (dienes and trienes) and triple bonds These are functional groups because chemistry can happen from them.

Answer 200

R – stands for or represents the rest of the molecule, usually referring to an alkyl group.

Answer 201

* Alcohols * Ethers

Answer 202

The simplest oxygen containing functional group. When carbon bonds to an oxygen with a hydrogen attached… The group bonded to the carbon is called a hydroxyl group, and the compound is an alcohol. The alcohol has an OH group replacing one hydrogen. R-OH

Answer 203

hydrocarbon chain: Ethanol – miscible with water (infinitely soluble). Hexanol – insoluble soluble in water.

Answer 204

Alcohols have the suffix –ol. We just follow the rules for alkanes, replacing e with –ol. Seven carbons means the structure is based on heptane. We include the number to differentiate from the other heptanols. The count from the other end (incorrectly) gives hepan-5-ol.

Answer 205

Alcohols are quite different to their parent carbon chains… Alcohols have much higher boiling points due to the hydroxyl group and the ability to hydrogen bond.

Answer 206

Industrial synthesis of alcohols uses the reactivity of the alkene functional group… This is done in the gas phase at high temperatures with a catalyst. Note how a hydrogen was added to one side and a oxygen (hydroxyl) to the other? This is an example of a reaction which alkenes can undergo called an addition reaction.

Answer 207

Methanol starting material for many reactions. Solvents – methanol, ethanol and propanol are common solvents. The word "alcohol" in alcoholic drinks refers to ethanol. Ethanol is commonly used as a disinfectant. Industrial methylated spirits are ethanol (with an additive). Fuels – methanol, ethanol, propanol, and butanol are especially interesting and can be synthesised chemically or biologically. Can the same oxygen bridge two carbons? Two carbon atoms join to the same oxygen form an ether. This molecule is diethylether, and was used as the first anaesthetic, called “ether”. Ethers have much lower boiling points than alcohols (ether b.p. 34.6 ºC). This is because they have no hydrogen-bonding ability and are less polar.

Answer 208

General formula R-O-R R’s may be same or different, R-O-R’ The shorter alkyl chain becomes the alkoxy substituent. The longer alkyl chain side becomes the alkane base name.

Answer 209

* Aldehydes * Ketones * Carboxylic acids (next lecture)

Answer 210

Yes! These are the carbonyl compounds. The carbon is double bonded to the oxygen. The chemistry of carbonyls is very different from alcohols and ethers.

Answer 211

‘shape shifters’ Carbonyl forms the basis for many other functional groups. The R-group is often a hydrocarbon (e.g. alkane, alkene or alkyne).

Answer 212

Aldehydes have the suffix –al. When you count the carbons make sure to include that of the aldehyde! Note: start numbering from the end that reaches the aldehyde/functional group soonest – giving the lowest number.

Answer 213

Ketones are named for the parent chain and a number for the ketone position (ketone suffix: -one)

Answer 214

Carboxylic acids are corrosive chemicals common in biological organisms. The carboxylic acid can be represented in structures as a line drawing, or as the formula.

Answer 215

Carboxylic acids have the suffix –oic acid. Note: no numbers are needed because…

Answer 216

Because they release a proton, yielding a carboxylate ion. When the proton is removed a negative charge is left behind. Preparing aldehydes, ketones, and carboxylic acids Aldehydes and carboxylic acids can be formed by the oxidation of primary alcohols. Ketones can be formed by the oxidation of secondary alcohols.

Answer 217

* Esters * Lipids * Triglycerides * Saturation in fats * Soaps

Answer 218

Esters look a bit like carboxylic acids but instead of an OH group they have an OR group Esters are made by condensation reactions

Answer 219

polarised and can be attacked by other atoms with spare electrons. The hydroxyl group (OH) of the carboxylic acid combines with the hydrogen of the alcohol to release water. This is a condensation reaction (loss of water).

Answer 220

For esters we split them into their component alcohol and acid. We name the alcohol part as an alkyl chain and give the acid part the suffix –oate.

Answer 221

The methyl esters (bottom row) related to the carboxylic acids above (top row) all have lower boiling points. This is because they do not hydrogen bond to each other like carboxylic acids do.

Answer 222

Esters are used as synthetic materials: polyesters. Esters often have strong smells, and are found in perfumes, scents and food flavourants. Esters are important in biology (fatty acid esters) and are found in fats and oils.

Answer 223

Esters can react with water to form an acid and an alcohol. This is the reverse of the ester formation reaction and is called hydrolysis (reaction with water). You can always tell what the components of an ester were by imagining a hydrolysis reaction happening.

Answer 224

Lipids are small biomolecules that are insoluble in water. They are major components of fats, oils, and cell membranes. They are isolated from living organisms by extraction with organic (non-polar) solvents.

Answer 225

ntermolecular forces determine whether a chemical (‘solute’) will dissolve in a particular liquid (‘solvent’). A generalisation for solubility is that: ‘like dissolves like’. When polar species (molecules or ions) dissolve in polar liquids they interact with the dipoles of the solvent, e.g. for a salt (like NaCl) in water:

Answer 226

dipoles for polar molecules to interact with.

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avoiding, don’t like contact with them.

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properties, rather than being related chemical structures. They can have different structures

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water, but soluble in organic solvent or non-polar solvents.

Answer 230

The combination of a polar head group with a long non-polar chain allows the formation of complex structures that can differentiate the outside from the inside by their solubility.

Answer 231

fats and vegetable oils. Animal fats are usually solid at room temperature. Vegetable oils are usually liquid at room temperature.

Answer 232

Lipids of this sort (fats and oils) are called triglycerides. The acyl-groups are long chains of carbon atoms. This gives the compounds their insolubility in water.

Answer 233

These long chains are typically between 12 and 20 carbon atoms long. They are long chain hydrocarbon acids (fatty acids). Three long chains are bound to a molecule of glycerol by ester bonds. Remember that the ester linkage is formed from an alcohol and a carboxylic acid. The alcohol which reacts with the three long chain acids is glycerol and it is a triol (an alcohol with three alcohol groups). This allows it to form three ester linkages in one molecule.

Answer 234

The ester bond can be hydrolysed with a strong base such as sodium hydroxide. Since the ester is formed from a glycerol molecule and three long chain acid molecules (fatty acids), these will be released. The three fatty acids can have different lengths. Longer chains can increase the melting points of triglycerides.

Answer 235

You might have heard about saturated fats, mono-unsaturated fats, and poly-unsaturated fats and their effects on health. What are they? We know that fatty acids can have alkane chains of different lengths. They can have double bonds too… Saturation of fats Alkanes are saturated because they have no double bonds. They cannot react with hydrogen – they are fullyhydrogenated

Answer 236

double bonds. They can react with hydrogen.

Answer 237

We classify fatty acids by how many double bonds they have Mono-unsaturated fats are triglycerides with three fatty acids, each having a long chain with only one double bond

Answer 238

Fats are solids while oils are liquids at room temperature. Why? Fats contain mostly saturated fatty acids. The fatty acid chains pack close together. This means the Van der Waals forces are stronger than in oils. The melting points of fats are higher than oils. Fats are solids while oils are liquids at room temperature. Why? Oils contain some unsaturated fatty acids. The fatty acid chains pack further away. The Van der Waals forces are weaker than in oils. This lowers the melting points of oils compared with fats.

Answer 239

Soap is made by hydrolysis of fats The fatty acid part is separated as the sodium salt – this is soap. Soap is a long hydrophobic chain ending in a carboxylic acid When a soap molecule binds to grease it does so because the grease particle is hydrophobic. The long soap tail orients towards the grease and the polar soap head points towards water. This arrangement of fats around something is called a micelle.

Answer 240

* Nitrogen-containing functional groups * Amines and amides * Amide-containing synthetic polymers * Amino acids and proteins

Answer 241

Nitrogen has 5 valence electrons. Nitrogen likes to form 3 single bonds to give neutral (uncharged) molecules, e.g. ammonia. Nitrogen shares 1 valence electrons in each of the three bonds to hydrogen. Leaving 2 electrons to form a lone pair. Recall that ammonia has a trigonal pyramidal shape.

Answer 242

amines Nitrogen can form up to three single bonds to carbon atoms to give neutral (uncharged) molecules. All the structures below are amines. We describe them by the number of carbon atoms bonded to N

Answer 243

Amines are named for the parent chain and a number for the amine position (amine suffix: -amine).

Answer 244

they H-bond in the liquid state.

Answer 245

NH3. In NH3, the nitrogen has 1 lone pair (and one more H) which can form 1 H-bond. The H-bond network is weaker than in H2O. Properties of 1° amines vs alcohols

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tetrahedral.

Answer 247

carboxylic acids, with the hydroxyl group replaced by an amine group.

Answer 248

stabilising a negative charge.

Answer 249

Amides are named for the parent chain and a number for the amide position (amide suffix: -amide). Bonding affects reactivity in amides Amides have the least reactive carbonyls of the carboxylic acid derivatives. The nitrogen in amides still has a lone pair. This gives amides some “double bond character” and helps to stabilise them: The partial positive character of the carbonyl carbon is smaller in amides than in esters, making this system less electrophilic.

Answer 250

Amides are less readily hydrolysed than esters: This is important in biology – proteins perform (nearly) all the important functions and processes in cells. These are polymers made of repeating amide bonds (from amino acids).

Answer 251

The 20 amino acids are the building blocks (monomers) that make-up the polymers we call proteins. They all have the same basic structure The different side-chains (R groups) are what give them their different properties. There are 20 different common amino acids. Amino acid side chains, combined with complex 3D shapes, are what give proteins their properties and functions. Amino acids: side chains Amino acids are classified according to their side chains A particular part of a protein can be hydrophobic by having lots of non-polar amino acids in one area.

Answer 252

Notice that the amino acid has both a carboxylic acid and an amine? We know that amines are basic and carboxylic acids are acidic. In zwitterions, the charges balance giving a neutral compound that is soluble in water.

Answer 253

Peptides are molecules containing at least one peptide bond (an amide bond between two amino acids). They are made by the condensation of amino acids The reverse reaction (hydrolysis) is slow When we write these, we can use the shorthand three letter code for each residue. Alanine-glycine becomes Ala-Gly

Answer 254

There are two possible peptides from alanine and glycine. The name order is important – Ala-Gly is different from Gly-Ala We “read” the sequences from N-terminus to C-terminus – from left to right. If we include more amino acid types the number of possibilities increases. If we use serine with alanine and glycine, there are nine (or 32) possible dipeptides

Answer 255

There are 20 amino acids so there are: 202 (=400) dipeptides possible 203 (=8000) tripeptides possible The median human protein length is 385 residues. For 20 different amino acids and a 385 residue protein there are 20385 possibilities. This is how all the different functions of proteins are possible using just 20 simple building blocks.

Answer 256

Proteins are large polymeric biomolecules constructed of many hundreds of amino acids held together by peptide bonds. Proteins perform (nearly) all the important functions and processes in all organisms. Your body is about 50% proteins by (dry) weight. Proteins have a large variety of functions: Biocatalysis (enzymes), transport of molecules, structural supports, gene regulation, physiological control (hormones), receptors, defence (antibodies), etc.

Answer 257

The structure of proteins starts with the peptide chain. The sequence of amino acids is called the primary protein structure. The peptide links are flexible, with free rotation about most bonds (the chain is floppy). As the chain begins folding –the hydrophobic residues “hide away” on the inside away from water. The protein is given structure by the interactions between chains. These interactions give the next layer of structure – called the secondary structure. H-bonding interactions give α-helices and β-sheets. Tertiary structure (“3D shape”) depends on how the primary and secondary structures are arranged in 3D space. Proteins can fold so that residues (amino acids) that are far apart in the chain become close to one another. This can create regions inside proteins where the environment is precisely controlled, a little “reaction vessel”, or active site.

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intramolecular interactions The tertiary structure interactions can be hydrogen bonds, ionic (between anions and cations) or covalent (-S-Slinkages).

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quaternary structure. Some proteins require many subunits to function properly e.g. ATP synthase. ATP is the energy currency in all living cells. Energy is ‘stored’ in the phosphate bond. Today we have learnt * What amines and amides are. * About synthetic and biological amide polymers.

Answer 260

particle with equal numbers of protons and electrons

Answer 261

sum of the number of protons and neutrons on the atom

Answer 262

equal to number of protons in the atom

Answer 263

subatomic particle that occupies most of the volume of the atom

Answer 264

subatomic particle with no charge

Answer 265

part of the atom that contains nearly all of the mass

Answer 266

positively charged subatomic particle

Answer 267

positively-charged ion

Answer 268

bond where electron pairs are shared between atoms

Answer 269

bond where two electron pairs are shared

Answer 270

the ability of a bonded atom to attract electrons to itself

Answer 271

bond between ions of opposite charge in a lattice

Answer 272

the regular repeating arrangement of atoms, ions or molecules in a crystal

Answer 273

bond where electrons are shared by cations in a lattice

Answer 274

group of covalently bonded atoms with no overall charge

Answer 275

partial charge on more electronegative atom in a bond

Answer 276

electrons on a bonded atom that are not involved in bonding

Answer 277

maximum number of bonds to hydrogen atoms

Answer 278

bond where electron pairs are shared unequally between atoms

Answer 279

endothermic

Answer 280

for a given equation describes the reaction of reactants to form products

Answer 281

heterogeneous

Answer 282

homogeneous

Answer 283

6.022 × 10 23 mol–1

Answer 284

mol is the unit for this quantity

Answer 285

mallest whole number ratio of atoms in a compound

Answer 286

excess reactant

Answer 287

limiting reactant

Answer 288

mass of one mole of substance in g mol–1

Answer 289

chemist's unit of amount (n)

Answer 290

formula showing all atoms in a molecule

Answer 291

percentage by mass of elements in a given mass of compound

Answer 292

sum of relative atomic masses of all atoms in the formula

Answer 293

relative numbers of atoms in a formula unit or reactants and products in a reaction

Answer 294

concentrated

Answer 295

Measure of amount of solute per volume of solution

Answer 296

Solution having the maximum mass of solute.

Answer 297

Maximum amount of solute in a specified volume of solution.

Answer 298

Substance in smaller amount in a solution

Answer 299

Homogeneous mixture of two substances

Answer 300

Substance in larger amount in a solution

Double Chem Exam Flashcards

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