Module Five - Equilibrium and Acid Reactions Flashcards
Static and Dynamic Equilibrium Factors that Affect Equilibrium Calculating the Equilibrium Constant (Keq) Solution Equilibria (144 cards)
1
Q
What is equilibrium?
A
is a state in which the rate of the forward reaction equals the rate of the backward reaction.
2
Q
What is enthalpy (ΔH)?
A
The total energy possessed by a chemical substance at constant pressure
3
Q
What is the formula to calulate the changing in enthalpy?
A
∆H𝑇𝑜𝑡𝑎𝑙 = Σ∆H𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − Σ∆H𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠
4
Q
What is entropy (ΔS)?
A
The measure of the randomness or disorder or chaos of a substance or a system.
5
Q
What is the formula to calculate the change in entropy?
A
∆𝑆𝑇𝑜𝑡𝑎𝑙 = Σ∆𝑆𝑝𝑟𝑜𝑑𝑢𝑐𝑡𝑠 − Σ∆𝑆𝑟𝑒𝑎𝑐𝑡𝑎𝑛𝑡𝑠
6
Q
What is Gibbs free energy (ΔG)?
A
Allows us to determine whether the reaction will occur spontaneously or not.
7
Q
How to determine if a reaction will occur spontaneously or not?
A
The Gibbs free energy (ΔG) determines this through:
ΔG=ΔH−TΔS
-∆𝐺 < 0, spontaneously
- ∆𝐺 > 0, not occur spontaneously
-∆𝐺 = 0, the reaction is in equilibrium and the concentrations of the products and reactants will remain constant
8
Q
What happens in a forward reaction?
A
Only the reactants react together to form the products.
9
Q
What happens in a reversible reaction?
A
Reactions, where the reactants are able to form products and the products, form reactants
10
Q
How do we know it’s a reversible reaction?
A
By using a two way arrow eg.
A + B ⇌ C + D
11
Q
What is a closed system?
A
When the chemicals in the reaction/matter are all contained within a certain space.
12
Q
What is an open system?
A
When the reaction substances/matter can either be added or lost to the surrounding environment.
13
Q
What is a physical change?
A
The products do not include any new substances. Instead, the physical properties of the reactant change, which can include a change of state.
eg. H2O(l) → H2O(g)
14
Q
What is a chemical change?
A
The reactants produce new substances with different properties. For this to happen, the atoms rearrange and form products that are different from the reactants. Eg.
2H2O(l) → 2H2(g) + O2(g)
15
Q
What is static equilibrium?
A
The reaction occurs in one direction and the reactants continue to produce the products until one of the reactants is used up and the reaction stops.
16
Q
What is an example of static equlibrium?
A
Diamond turning into graphite
17
Q
What is dynamic equilibrium?
A
As the products are formed, some of them will react to become reactants again. This means that when the reaction appears ‘complete’, there are both reactants and products present.
18
Q
What is an example of a dynamic equilibrium?
A
Decomposition of nitrosyl bromide into nitric oxide and bromine gas in a closed container
2NOBr (g) ⇌ 2NO (g) + Br2 (g)
19
Q
Are all physical changes reversible reactions?
A
Yes
20
Q
Are all chemical change reversible reactions?
A
No, only some
21
Q
What is a forward reaction?
A
The reaction where the reactants form products
22
Q
What is a reverse reaction?
A
The reaction where the products form reactants.
23
Q
What is Collision theory?
A
States that for a reaction to occur, the particles must collide with sufficient energy to break the bonds and have the appropriate orientation to allow the new bonds to form
24
Q
What is the activation energy?
A
Amount of energy required to break the bonds of the reactants (Ea)
25
What is the activated complex
This is the difference in enthalpy between the reactants
26
If the reactant particles in a collision do not have enough energy to break the bonds, then they are unable to form the products? True/False
True
27
If the activation energy is lower, do particles have enough energy to break the reactant bonds to form products
Yes
28
What are the conditions for a chemical system to reach equilibrium?
-is a closed system
-involves a reversible reaction.
-At equilibrium, the:
-rate of the forward reaction is the same as the rate of the
reverse reaction
-concentrations of the reactants and products remain
-constant macroscopic properties are constant.
29
How to determine whether the reaction will occur spontaneously or not? Equation
ΔG=ΔH−TΔS
When ΔG is:
-negative, the reaction will occur spontaneously
-positive, the reaction will not occur spontaneously.
30
Is the Gibbs free energy for photosynthesis reaction spontaneous
No
31
Does photosynthesis only occur during the day when the UV energy from the sun is readily available?
Yes
32
What is respiration?
- Respiration is the combustion reaction of glucose.
| - The reactants and products of respiration are the reverse of those of photosynthesis.
33
Is the Gibbs free energy for respiration negative and why does respiration occur?
Yes, thus Gibbs free energy will occur spontaneously. This reaction occurs every day in our bodies to provide the energy we need to live.
34
What does it mean when Gibbs free energy for a reaction is very close to zero?
Indicate that the reactants could form products, while at the same time the products could react to form the reactants. Thus is a reversible reaction.
35
How to graph a concentration and time graph?
- reactants are initially large
- products are initially zero
- reactants decrease initially quickly (steep graph) and then more slowly
- products increase initially quickly (steep graph) and then more slowly
- all will plateau when the system reaches equilibrium.
36
How to graph a rate and time graph?
- forward reaction is initially high
- reverse reaction is initially zero
- forward reaction will decrease quickly initially but then more slowly
- reverse reaction will increase quickly initially but then more slowly
- two reactions will become equal this is when equilibrium is reached.
37
What is the difference between the concentration vs time and reaction rates vs time in terms of the number of lines?
C vs T
- any number depending on the number of reactants and products
- each is represented on the graph by a separate line
R vs T
-Two lines, forward and reverse reaction
38
What is the difference between the concentration vs time and reaction rates vs time in terms of the position of line at equilibrium?
C vs T
-All lines become horizontal as concentrations are constant. They do not need to be of equal value.
R vs T
The two lines meet and plateau as the two rates are equal.
39
What does Le Chatelier's principle (LCP) use to predict?
Predicts the changes that will occur following a change in the conditions (concentration, pressure, volume or temperature of a system)
40
What does LCP state?
‘If a system at equilibrium is subject to a change in conditions, then the system will behave in such a way so as to partially counteract the imposed change.’
41
What happened when concentration is altered according to LCP?
- An increase in reactants causes a shift to the right (towards products).
- An increase in products causes a shift to the left (towards reactants).
42
What happened when pressure is altered according to LCP?
- An increase in pressure causes a shift to the side with fewer moles of gas.
- A decrease in pressure causes a shift to the side with more moles of gas.
43
What happened when the volume is altered according to LCP?
- A decrease in volume, causes a shift to favour the side of fewer moles of gas.
- An increase in volume causes a shift to the side with more moles of gas.
44
What happened when there is an addition of an inertia gas (argon or krypton) according to LCP?
Nothing will happen to equilbirum position.
45
What happened when the temperature is altered according to LCP for endothermic?
- An increase in temperature causes the equilibrium will shift to the right.
- A decrease in temperature causes the equilibrium will shift to the left.
46
What happened when the temperature is altered according to LCP for exothermic?
-An increase in temperature will shift the equilibrium to the left
A decrease in temperature will shift the equilibrium to the right.
47
What is an exothermic reaction?
The products have less enthalpy than the reactants, meaning
| that energy will be released to the surroundings.
48
What is an endothermic reaction?
The reactants have less enthalpy than the products and therefore energy will be absorbed from the surroundings.
49
Does the addition of a catalyst affect equilibrium?
No, but t does affect how quickly equilibrium is attained.
50
Does a catalyst decrease the activation energy of both the forward and reverse reactions equally?
Yes
51
When there is an increase in the concentration of the system is there a change on the graph?
Yes, there will be a sudden increase in one substance
52
When there is a decrease in the concentration of the system is there a change on the graph?
Yes, there will be a sudden decrease in one substance.
53
When there is an increase in the volume/decrease in pressure of the system is there a change on the graph?
Yes, a sudden decrease in all gaseous species
54
When there is a decrease in the volume/increase in pressure of the system is there a change on the graph?
Yes, a sudden increase in all gaseous species.
55
When there is an increase in the temperature of the system is there a change on the graph?
No sudden changes
56
When there is a decrease in the temperature of the system is there a change on the graph?
No sudden changes
57
When there is an addition of a catalyst to the system is there a change on the graph?
Reaches the same equilibrium position in a shorter time.
58
What is the equilibrium constant (K or Keq) formula?
Keq = [products] / [reactants]
59
When can Keq be used for a chemical reaction?
If the concentrations of the chemical species are measured for that reaction when it has reached equilibrium.
60
When can the reaction quotient(Q) be used for a chemical reaction?
If the concentrations of the chemical species are measured for a reaction that has not reached equilibrium.
61
How to use Q to determine equilibrium?
- If Q < Keq, the forward reaction will be favoured to reach equilibrium.
- If Q > Keq, the reverse reaction will be favoured to reach equilibrium.
- If Q = Keq, then the system is at equilibrium.
62
How to predict the position of equilibrium using Keq?
- If Keq > 1, the equilibrium lies to the right.
| - If Keq < 1, the equilibrium lies to the left.
63
What happened to the equilibrium expression when the chemical equation is reversed?
It is inverted.
Eg chemical equation change from 2H2(g) + O2(g) ⇌ 2H2O(g) to 2H2O(g) ⇌ 2H (g)+O (g)
Keq = [H2O]^2 / [H2]^2[O2] turns into Keq = [H2]^2[O2] / [H2O]^2
64
What happened to the equilibrium expression when the chemical equation is reversed?
It is inverted.
Eg chemical equation change from 2H2(g) + O2(g) ⇌ 2H2O(g) to 2H2O(g) ⇌ 2H (g)+O (g)
Keq = [H2O]^2 / [H2]^2[O2] turns into Keq = [H2]^2[O2] / [H2O]^2
65
What are the units for equilibrium constants?
molL−1
66
What is colourimetry?
Is a quantitative technique used to measure the difference in the darkness or lightness of the colour of a solution.
67
How does colourimetry work?
Coloured solutions absorb light; hence, more light enters the solution than exits it. The amount of light absorbed by the solution is called absorbance. This is related to the concentration of the solution.
68
Which theory relates to colourimetry?
The Beer-Lambert law states the quantitative relationship between absorbance and concentration:
A=εlc
where:
A = absorbance (ratio between light entering and
existing the solution)
ε = molar absorbtivity (measure amount of light)
l =is the path length of the light through the sample
c =is the concentration of the solution
69
How to use solubility product (Ksp) to predict precipitation?
-If the ionic product = Ksp, then the system is at equilibrium.
-If the ionic product < Ksp, the forward reaction would be favoured and the solid would dissolve for the
system to reach equilibrium.
-If the ionic product > Ksp, the reverse reaction would be favoured and more precipitate would form for the system to reach equilibrium.
70
What is the dissociation of acids?
-In some acids, all of the molecules ionise in water to form their ions. E.g
CH3COOH(aq) +H2O(l) ⇌ H3O (aq)+CH3COO (aq)
-However, in other acids, only some of the molecules ionise. E.g
CH3COOH(aq)⇌ H (aq) + CH3COO (aq)
71
What is the dissociation of a base?
A weak base is a base where only some of the molecules of the base react with water to produce ions. Eg
NH3(aq) + H2O(l) ⇌NH4(aq) + OH(aq)
72
What can equilibrium constants for the gaseous system be expressed by?
It can be express in terms of pressure Kp
73
What units can be used to express pressure?
atmospheres (atm), kilopascals (kPa) or millimetres of mercury (mmHg)
74
What are the two important terms that you need to understand before looking at equilibrium systems?
1. mole fraction
| 2. partial pressure
75
What is a mole fraction?
The ratio of the number of moles of a particular gas to the number of moles of gas in the total present in a gaseous mixture.
76
What is the general equation for the mole fraction?
Mole fraction of gas A = Number of moles of gas A / Total number of moles of gas present
77
What is partial pressure?
Is the proportion of the pressure that
| is due to the collisions for a particular gas present.
78
What is the general formula for partial pressure of a gas in a system?
The partial pressure of gas A = Mole fraction of gas A × Total pressure of the system
79
What is the expression for the equilibrium constant in terms of pressure (Kp) of the equation: aA(g) + bB(g) ⇌ cC(g) + dD(g)?
Kp = P^a A × P^b B / P^c C × P^dD
80
When writing the expression for the equilibrium constant in terms of Kp do we use square brackets?
No, because square brackets are used to indicate concentration.
81
What is the structure of ionic compounds?
They have a crystalline structure in which the positive and negative ions are arranged in an orderly fashion with every positive ion being surrounded by negative ions and every negative ion being surrounded by positive ions.
82
What is water composed of?
Two hydrogens atoms covalently bonded to an oxygen atom.
83
Is water a polar molecule?
Yes, because there is a large difference in electronegativity between the oxygen and hydrogen atoms within the molecule.
84
Why is water a polar molecule?
Oxygen’s strong ability to attract electrons means that the electrons in the O—H covalent bond are more attracted to oxygen. Oxygen becomes slightly negatively charged and hydrogen is left with a slightly positive charge. The hydrogen atom is so small that it also means that two molecules can get very close to each other.
85
When does the water of crystallisation occur?
When water molecules are attracted to the ions of a salt.
86
What are bonds between the ions and water called?
Ion-dipole bonds, the ion and the dipole in the water molecule forms a weak bond.
87
What are water or other molecules that form dipole bonds to a metal atom called?
Ligands
88
What is anhydrous?
Salts that do not have water of crystallisation.
89
What does solubility depend on?
1. energy required to separate ions from lattice
2. energy release as the released charged ions become hydrated
Therefore the more energy released compared with the energy needed, the more soluble the salt.
90
What is a saturated solution?
The solution in which no more of a particular solute can dissolve in a given quantity of solvent.
91
What is a supersaturated solution?
An unstable solution that has more than the maximum amount of solute dissolved in a given quantity of solvent; it has a higher amount of solute than the saturated solution.
92
What is an unsaturated solution?
a solution where all of the solutes dissolves; it has not reached dynamic equilibrium.
93
What is the solubility of a solute?
Is the maximum mass in grams that can dissolve in 100 g of the solvent at a given temperature.
94
What do solubility curves show?
How much of a solute, such as salt, can be dissolved at a particular temperature.
95
What are toxins?
Referred to substances that had harmful effects on people or even caused death, while unpalatable substances had either an unpleasant taste or smell.
96
What are unpalatable substances?
unpalatable substances had either an unpleasant taste or smell.
97
What are cycad and why are they important to the Aboriginal and Torres Strait Islander Peoples?
Cycad is toxic fruit that Aboriginal and Torres Strait Islander Peoples mainly consume. However, it leads to gastrointestinal, liver disorders, including cancer and death.
98
What methods are used to remove the toxins in cycad fruits?
1. Leaching involves the use of water to dissolve the toxin and remove it from the plant. Hence, it is used when the toxins are water-soluble and there is a readily available water supply. This process could take as little as a few hours or as long as several days.
2. Cut open the fruit and leave the fruit in water.
99
Whare are the solubility rule?
```
-NAGSAG, PMS, and CASTROBeAR
• Nitrates (NO32-) are always soluble
• Acetates (C2H3O2-)are always soluble
• Group 1 ions are always soluble
• Sulphates (So42-) are always soluble
• Ammonium (NH4+) is always soluble
• Group 7 ions are always soluble
Exceptions:
• PMS: Pb2+ , Mercury, Silver
• CASTROBeAR:Calcium(Ca2+),Strontium
(St2+), Barium (Ba2+) From these mnemonic devices, you can answer all solubility questions.
-Recall that more active metals will replace less active metals in solution.
```
100
What are aqueous solutions?
When ionic substances dissolve in water, they dissociate. This means they separate into their ions, which are then able to move freely and independently of each other through the solution. Eg NaCl(s) --> Na+ + Cl-
101
Does 'soluble’ means that a compound dissolves to more than 10gL−1 (or 1g/100mL)? True/False
True
102
Does 'insoluble’ means that it dissolves to less than 10 g L−1 ( 1g/100ml)? True/False
False as insoluble means to dissolve less than 1g L-1
103
Does ‘sparingly soluble’ means that it dissolves in the range 1gL−1 to 10gL−1? True or False
True
104
What is a precipataion reaction?
When solutions of certain ionic compounds were mixed, they sometimes reacted to produce a solid called a precipitate.
105
What are spectar ions?
Ions that are not involved in a reaction.
106
What are the steps to determine if a precipate forms?
To determine if a precipitate forms:
1. Find the limiting reagent.
2. Calculate the solubility. (Q)
3. Determine whether there is a precipitate remaining by comparing Ksp from the datasheet.
If Q < Ksp, no precipitate will form. (saturated solution)
If Q = Ksp, a precipitate will form.
If Q > Ksp, a precipitate will form. (supersaturated
solution)
107
Why are precipation reactions are useful for finding out whether a particular anion or cation is present?
Chemists could use precipitation reactions to test for lead or cadmium in water supplies. Precipitation reactions can also be used to remove unwanted substances from water.
108
What is molar solubility?
When a salt is dissolved in distilled water, there is a direct relationship between the solubility product and the concentration of each of the ions measured in mol L−1.
109
Does molar solubility only occurs when there are no other contaminants present, and only the salt and water are present? True/False
True
110
What are the steps in using molar solubity to determine the Ksp?
1. write a balanced equation for the solubility of the salt
2. convert solubility data into mol L-1 (find n)
3. determine the concentration for each of the ions (mole ratio)
4. write equilibrium expression (Ksp)
5. substitute data into the expression to calculate the Ksp
111
What is the common ion effect?
Is when a common ion is added to a saturated solution that decreases the solubility of the salt
112
What is intermolecular forces?
Intermolecular forces are forces that exist between molecules. It consists of dispersion, dipole-dipole and hydrogen bonding forces
113
What are despersion forces?
These are the hardest to conceptualise and are also the weakest inter-molecular force.
114
What are dipole-dipole forces?
These are stronger than dispersion forces, and occur when polar substances (that is, substances that always have a positive dipole and a negative dipole)
115
What are hydrogen bonds?
These are exactly the same as dipole-dipole intermolecular forces, however, are much stronger. They occur when a positive dipole (hydrogen) lines up with extremely electronegative negative dipoles (you can remember this as FON: fluorine, oxygen, or nitrogen!).
116
What is an example of static equlibrium?
Diamond turning into graphite
117
What is a combusion reaction?
a hydrocarbon reacts with oxygen to release carbon dioxide and water alongside heat. In other words, combustion is always exothermic.
118
How to distinguish if the entropy of a combustion increases? ( ∆𝑆 > 0)
When there are more gas molecules in the products
119
Why is the enthalpy of combustion reactions negative (∆H < 0)
Because it's an exothermic reaction.
120
What is photosynthesis and the formula?
In photosynthesis, carbon dioxide and water is used to form glucose and oxygen
6CO2 (g) + 6H2O (l) + Sunlight (UV) → C6H12O6 (s) + 6O2 (g)
121
Why does the entropy of photosynthesis decrease?
Because the reacts have 6 molecules of gas and 6 molecules of liquid while the products have 6 molecules of gas and 1 molecule of solid. Therefore the reactants have more molecules then products.
note: S solids < S liquids < S gases
122
Why is the enthalpy of photosynthesis reactions positive (∆H < 0)
Because it's an endothermic reaction
123
What is the Haber process?
The reaction of nitrogen and hydrogen to form ammonia.
| N2 (g) + 3H2 (g) ⇌ 2NH3 (g)
124
What is the heating cobalt(II) chloride hydrate reaction?
When cobalt(II) chloride is dissolved in water, the pink Co2+ (aq) ion forms in equilibrium with the blue ion CoCl42-.
Co(H2O)62+ (aq) + 4Cl– (aq) [pink] ⇌ CoCl42– (aq) + 6H2O (l) [blue]
125
Is the heating cobalt(II) chloride hydrate reaction reversible?
Yes
126
When is the heating cobalt(II) chloride hydrate exothermic and endothermic?
The forward reaction is endothermic while the reverse reaction is exothermic.
127
What happens when heat is added to the solution of cobalt(II) chloride hydrates is heated?
When heat is added to the solution, the equilibrium will shift to the right to absorb some of
the heat. Therefore, the solution will become more blue.
128
What happens the solution of cobalt(II) chloride hydrates is placed in ice?
When the solution is placed in ice, the equilibrium will shift to the left to add more heat to
the system. Therefore, the solution will become pinker.
129
When is the interaction between nitrogen dioxide and dinitrogen tetroxide exothermic and endothermic?
exothermic in the forward direction and endothermic in the reverse direction.
2NO2 (g) ⇌ N2O4 (g)
130
What happens when the temperature for the interaction between nitrogen dioxide and dinitrogen tetroxide increases?
Increasing the temperature will favour the reverse (endothermic) reaction and increase the concentration of nitrogen dioxide, which is a brown colour. The gas will become a darker colour.
131
What happens when the temperature for the interaction between nitrogen dioxide and dinitrogen tetroxide decreases?
Decreasing the temperature will favour the forward (exothermic) reaction and increase the concentration of dinitrogen tetroxide, which is colourless. The gas will become a lighter colour.
132
How does changing the volume of the interaction between nitrogen dioxide and dinitrogen tetroxide causes the reaction to favour one side? (reverse or forward reaction)
- Increasing volume (decreasing pressure) will favour the reverse reaction
- Decreasing volume (increasing pressure) will favour the forward reaction
133
What happens when iron (III) nitrate reacts with potassium thiocyanate?
An equilibrium mixture of Fe+3, SCN–, and the complexion FeSCN+2 is formed.
134
What experiments are required to determine the Keq of iron (III) thiocyanate?
stoichiometry and spectrophotometric analysis to determine the equilibrium constant for a reaction between iron(III) ion (Fe3+) and thiocyanate ion (SCN–).
135
Is iron (III) nitrate and potassium thiocyanate a reversible reaction?
Yes
| Fe3+ [pale yellow] + SCN- [colourless] ⇌ FeSCN2+ [reddish brown]
136
What happens when you add some SCN- ions in the iron (III) nitrate and potassium thiocyanate reaction
Would cause some Fe3+ ions to react with it and the equilibrium shifts from right to left and the red colour of the solution deepens.
137
What is the burning magnesium reaction an example of?.
It is an example of a combustion reaction.
138
Is burning magnesium a reversible reaction?
No, after it burns, it forms a white powder.
| 2Mg + O2 → 2MgO
139
What is burning steel wool an example of?
It is an example of a combustion reaction
140
Is burning steel wool a reversible reaction
No, steel wool is actually mostly iron and if reacted with oxygen in the air it will form iron oxide which is irreversible.
4Fe + 3O2 → 2Fe2O3
141
What happens when potassium chloride is reacted with silver nitrate?
Resulting in the formation of silver chloride which is a white precipitate.
KCl + AgNO3 → AgCl + KNO3
142
What happens when potassium iodide and lead nitrate react?
a double-replacement reaction happens. The two compounds react, and the positive ions and negative ions of the two reactants switch places, creating two new compounds Lead particles and iodide particles combine and create two new compounds, a yellow solid called lead iodide and a white solid called potassium nitrate.
KI + PbNO3 → KNO3 + PbI2
143
What happens when sodium sulphate and barium nitrate react?
Form one soluble salt, sodium nitrate, and an insoluble salt, barium sulphate. Barium sulphate is one of the most insoluble compounds known.
Na2SO4 + Ba(NO3)2 → BaSO4 + NaNO3
144
Q: Calculate the solubility product constant for lead(II) chloride, if 50.0 mL of a saturated solution of lead(II) chloride was found to contain 0.2207 g of lead(II) chloride dissolved in it.
1. PbCl2(s) ⇌ Pb2+(aq) + 2Cl-(aq)
Ksp = [Pb2+][Cl-]^2
2. n(PbCl2) = 0.2207 / 278.1
3. [PbCl2] = 7.93x10^-4 / 0.005 = 0.0159M
4.Therefore [Pb2+] = 0.0159M and [Cl-] = 2 x 0.0159 = 0.0318M (ratio, 1:2)
5. Ice table to fin d equilibrium concentration
6. Ksp = [0.0159][0.0318]^2 = 1.61 x10^-5
