topic test three Flashcards
(37 cards)
1
Q
what is energy
A
the capacity to do work or cause change
- energy change: due to bond breaking / forming
- stored energy: due to attractive and repulsive forces between particles
2
Q
what is a system / surroundings
A
- system: reactant and products
- surroundings: everything surrounding / outside of the system (not included in the reaction)
3
Q
what is the law of conservation of energy
A
- states that energy cannot be created or destroyed
- can be transferred / changed from one form to another
4
Q
What is bond breaking and forming
A
In nearly all reactions intermolecular and intramolecular forces/bonds are broken in the reactants to form new products
5
Q
What is an exothermic reaction
A
- reaction that causes temperature of system to rise consequently heat flows out of the system (into surroundings)
- reacting system loses energy to the surroundings thus enthalpy decreases
- enthalpy change is negative
6
Q
What is an endothermic reaction
A
- reaction that cause temperature of system to fall, consequently heat flows into the system (gains heat from surroundings)
- reacting system gains energy from surroundings thus enthalpy decreases
- enthalpy change is positive
7
Q
what are physical changes
A
- involve breaking / making of weak bonds
- require small amounts of energy
- state changes (melting, boiling, freezing, dissolving, vaporisation)
8
Q
what are chemical changes
A
- involves breaking / forming of strong chemical bonds
- large amount of energy is required
- when new products are being formed
9
Q
what is enthalpy
A
- total energy present in the substance
- different reactions have different enthalpies as strength of bonds varies depending on each substance
10
Q
what is the amount of enthalpy in a system
A
- the amount of energy released / absorbed by surroundings
11
Q
what is change in enthalpy
A
- /\H is measure in kJ
- /\H = H(products) - H(reactants)
12
Q
what is the transition state / activated complex
A
- maximum potential energy (Ep) in the reaction
- represents stage where bond breaking (endo) and forming (exo) occurs
- unstable and exists temporarily, once formed changes quickly to products or returns to reactants
13
Q
what is the activation energy
A
- Ea: minimum amount of energy required for a successful collision which results in a reaction occurring
- referred to as Ea barrier which must be overcome for a reaction to occur
14
Q
how does one measure rate of reaction
A
- amount of substance use or produced / time taken
15
Q
what is the collision theory
A
- collision must occur for a chemical reaction to occur
- minimum specific amount of energy and favourable orientation is required for successful collisions
16
Q
what are the factors affecting ror
A
- temperature: ^temp = ^kinetic energy of reacting particles and distribution of molecules (^velocity / movement / successful collisions / sufficient energy to overcome Ea)
- subdivision: ^SA (makes reactants smaller) = ^exposure to reactants / more collisions in given space (more successful collisions / Ea)
- nature: gases (more complex bond breaking / forming), solutions (no energy required to break intermolecular bonds)
- catalyst: provides alternate pathway with lower Ea (^successful collisions / sufficient Ea)
- concentration: ^c = ^ particles / collisions / Ea
- pressure: ^p = ^con. of particles (^ collisions / Ea)
17
Q
explain the bonding involved in water
A
- covalent (intramolecular) bonds between H and O atoms
- weak dispersion forces (weakest intermolecular force) between water molecules
- hydrogen bonding (strongest intermolecular force, but still much weaker than covalent) between water molecules
18
Q
what are dispersion forces
A
- polar: electrostatically attracted to other molecules (one side of the molecule being slightly more positive and the other slightly more negative)
- non polar: (no overall charge distribution) the molecules still need to be attracted to each other
- e are always moving: spend more time in one area than another, area becomes temporarily more -ve (other side temporarily more +ve)
- if non-p comes close to another molecule which has temporary +ve/-ve sides (dipole), temporary attraction occurs, happens throughout substance.
19
Q
MP and BP of water
A
- MP: 0C
- BP: 100C, intermolecular forces (force between molecules) are broken, covalent bond holding H and O atoms together are not broken
- BP: is high compared to other molecular compounds (H bond is strongest intermolecular force)
20
Q
surface tension as a property of water
A
- very high
- molecules are held together relatively strongly (H bonding occurring in all directions)
- surface layer there is no water molecules above to ‘pull up’ these molecules so the surface molecules tend to be pulled back into the liquid
21
Q
density as a property of water
A
- liquid: cool water is denser than warm water, particles move closer tougher in a smaller amount of space
- solid: less sense than water, molecules slow right down, for, more H bonds which holds the, in an open hexagonal structure (prevents close packing)
22
Q
what is solubility
A
- the extent to which a solute will dissolve in a solvent
23
Q
polar and non polar solutes
A
- P: polar solute dissolves in polar solvent, are hydrophilic (water loving), dissolve in water
- NP: np solute dissolves in np solvent, are hydrophobic (water hating), don’t dissolve in water
24
Q
what are factors affecting solubility
A
- amount, nature, temperature, pressure of solvent / solute
- temp: solids and liquids (^temp = ^solubility), gases (decreased temp = ^ solubility)
- pressure: little affect on solids and liquids, decreased pressure of gas = decreased solubility
25
what are electrolytes
- a produces ions in a solution
- ionic substances dissociate (break down) to form ions
- covalent substances ionise (break down) to form ions
- strong: completely dissociate and partially ionise
- weak: partially ionise (double arrow)
- non: do not dissolve in water
26
what is concentration
- strong solution has more particles than a weak in the same amount of solvent
- [ppm] = m(solute mg) - m(solution kg)
- calculations: n=cV, m=cV, n=m/M
27
types of concentrated solutions
- unsaturated: contains less solute than it is able to dissolve at a given temperature
- saturated: contains as much solute as it can dissolve at a given temp / pressure
- supersaturated: contains more solute than a saturated solution under existing conditions
- stable/unstable: when temp changes some compounds release excess solute / some are stable and don't
28
what is an acid
- pH more than 7
- sour, turns blue litmus paper red, corrosive, conduct electricity, react with carbonate to form CO2, react with some metals to form H2, react with bases to form water
- common acids: HCl, H2SO4, H2SO3, CH3COOH, H2CO3, HNO3, NH4CO3, NH4NO3, C6H8O7, CH3CH(OH)COOH
29
what is a strong acid / weak acid
- strong: completely ionise to produce ions in solution
- e.g. HNO3 (nitric), H2SO4 (sulfuric), HCl (hydrochloric), HBr (hydrobromic), HI (hydroiodic) HClO4 (perchloric)
- other acids (weak): partially ionise (ethanoic, hydrofluroic, carbonic)
30
what is a base
- pH >7, taste bitter, turns red litmus paper blue, can be corrosive, conduct electricity, feel slippery, do not react with most metals, react with acids to form water
- common bases: NaOH, NH3, Ca(OH)2, NaHCO3, CaO, Na2CO3
31
what are strong / weak bases
- strong bases: completely dissociate to produce OH ions (group I / II and metal OH)
- other bases (weak): carbonates, ammonia, other hydroxides are completely dissociated
32
what is Arrhenius's theory
- states that an acid is a substance that will ionise in solution producing H (aq) ions
- a base is a substance that will dissociate in solution releasing OH (aq) ions
- neutralisation: acidic (H) and basic (OH) = neutralisation
33
what are the limitations of Arrhenius's theory
- some substances behave as bases (produce OH ions in solution) that do not contain OH in their formula (NH3, CO3)
- only applies to acids / bases in water and not in other solvents
- some reactions cannot be explained
- not all salts are neutral, can be basic or acidic
- H+ ion cannot exist for very long in water
- H (aq) + H2O (l) --> H3O+ (aq) (hydronium ion): in an aqueous solution, an acid should said to produce H3O + (aq) ions
34
what is the bronsted-Lowry theory
- states that transfer of hydrogen ion (proton) from one reactant to another. acid loses proton (H+) proton donor and base gains proton (H+) proton acceptor
35
what is pH
- measure of concentration of hydrogen ions, a neutral solution has equal concentrations of H and OH ions
36
explain self ionisation in water
- H2O (l) + H2O (l) H3O+ (aq) + OH- (aq)
- at 25C, c(H3O+) = 1 x 10-7 mol/L, since H3O+:OH- is 1:1, c(OH-) must also be 1 x 10-7 mol/L
- neutral: c(H3O+) = 1 x 10-7 mol/L, c(OH-) = 1 x 10-7 mol/L
- acidic: c(H3O+) > 1 x 10-7 mol/L
- basic: c(OH-) > 1 x 10-7 mol/L or alternatively, c(H3O+)
37
logarithms and pH
- pH = - log [H+], therefore [H+] = 10-pH
