09 Chemical Equilibria, Set A To print: Ctrl + P, paper A4, margins Default.
Learners' AlleyDesigned by Khow Willard
09
Chemical Equilibria
Set AFoundations
Name
Time 1 hour
Total 34 marks
A Data Booklet may be used.
A
From the lesson
13 marks
1
CommonWrite Kc and Kp, with units, for N2(g) + 3H2(g) ⇌ 2NH3(g).
[2]
Source: Learners' Alley, Chemical Equilibria slides
2
ChallengeWrite Kc for Fe3+(aq) + 3H2O(l) ⇌ Fe(OH)3(s) + 3H+(aq).
[1]
Source: Learners' Alley, Chemical Equilibria slides
3
Common1.00 mol of H2 and 1.00 mol of I2 are heated in a 1.00 dm3 flask: H2(g) + I2(g) ⇌ 2HI(g). At equilibrium there is 1.56 mol of HI. Find Kc.
[2]
Source: Learners' Alley, Chemical Equilibria slides
4
CommonPredict the effect of increasing pressure on the position of equilibrium in each of the following. All species are gases.
(a)
N2 + 3H2 ⇌ 2NH3
[1]
(b)
H2 + I2 ⇌ 2HI
[1]
(c)
PCl5 ⇌ PCl3 + Cl2
[1]
Source: Learners' Alley, Chemical Equilibria slides
5
Define dynamic equilibrium.
[1]
Source: Learners' Alley, Chemical Equilibria slides
6
Write Kc for 2SO2(g) + O2(g) ⇌ 2SO3(g), with units.
[1]
Source: Learners' Alley, Chemical Equilibria slides
7
Why does a catalyst not change the yield?
[1]
Source: Learners' Alley, Chemical Equilibria slides
8
Why is 450 °C used in the Haber process, not a lower temperature?
[2]
Source: Learners' Alley, Chemical Equilibria slides
B
Practice
21 marks
9
CommonThe equation describes the equilibrium between some gases. 2NO(g) + 2H2(g) ⇌ N2(g) + 2H2O(g) ΔH < 0
Which of the changes increase the Kp of the reaction?
1Decreasing the volume of the reaction vessel2Decreasing the temperature of the system3Injecting more hydrogen gas into the reaction vessel
A2 only
B1 and 3 only
C2 and 3 only
D1, 2 and 3
Answer [1]
Source: IJC 2017 Promo, via Chemical Equilibria Topical Revision Booklet, Q4
10
In the industrial production of nitric acid, the first step involves the oxidation of ammonia to nitrogen oxide. 4NH3(g) + 5O2(g) ⇌ 4NO(g) + 6H2O(g) ΔH < 0
Which of the following would favour the oxidation of ammonia?
Aremoval of H2O
Baddition of catalyst
Cincrease in temperature
Dreduction in the volume of the system
Answer [1]
Source: IJC 2017 Promo, via Chemical Equilibria Topical Revision Booklet, Q6
11
For the reaction 2X2(g) + Y2(g) ⇌ 2X2Y(g), the value of the equilibrium constant Kc is 5.00. Determine the value of Kc for each of the following equilibria, including its units.
(a)
4X2(g) + 2Y2(g) ⇌ 4X2Y(g)
[1]
(b)
X2Y(g) ⇌ X2(g) + ½Y2(g)
[1]
Source: EJC 2022 JC1 Chemical Equilibria Tutorial, A6
12
A mixture contained 1.00 mol of ethanoic acid and 5.00 mol of ethanol. After the system had come to equilibrium, a portion of the mixture was titrated against 0.200 mol dm−3 sodium hydroxide solution. The titration showed that the whole of the equilibrium mixture would require 289 cm3 of the standard alkali for neutralisation. Find the value of Kc for the esterification reaction, CH3COOH(l) + C2H5OH(l) ⇌ CH3COOC2H5(l) + H2O(l).
[3]
Source: EJC 2022 JC1 Chemical Equilibria Tutorial, A7
13
CommonIndustrially, coal can be converted into a combustible gas by passing steam over white hot coke. H2O(g) + C(s) ⇌ H2(g) + CO(g) ΔH = +131 kJ mol−1
(a)
Write an expression for the equilibrium constant, Kp, including its units.
[1]
(b)
How would the composition of the equilibrium mixture change if there were an increase in pressure and in temperature respectively? Explain your answer.
[2]
(c)
Steam was passed over coke at 730 °C. At equilibrium, pH2O is 90 kPa and pH2 is 183 kPa. Calculate the equilibrium partial pressure of carbon monoxide and hence Kp. If the steam is now brought to a new equilibrium partial pressure of 150 kPa by compression of the whole vessel, what will be the new equilibrium partial pressure of hydrogen?
[3]
Source: EJC 2022 JC1 Chemical Equilibria Tutorial, A9(a) to (c)
14
Zinc oxide can be produced from zinc and steam. Zn(s) + H2O(g) ⇌ ZnO(s) + H2(g) ΔH < 0. 2.60 mol of zinc and 2.60 mol of steam are placed in a sealed vessel and heated. At equilibrium, 2.58 mol of zinc oxide is produced. The total pressure at equilibrium is 10 atm.
(a)
Calculate the partial pressure of H2 at equilibrium.
[1]
(b)
Write the expression for the equilibrium constant, Kp, of this reaction. Use your expression to calculate the value of Kp.
[2]
(c)
Explain how a decrease in temperature affects the yield of zinc oxide.
[1]
Source: 2023 RI J2 Prelim P2 Q5(e)
15
ChallengeThe Fischer–Tropsch process is one method of manufacturing methane. CO(g) + 3H2(g) ⇌ CH4(g) + H2O(g). A mixture of CO and H2 in the molar ratio 1 : 3 is added into a sealed vessel and heated to 800 °C. At equilibrium, the total pressure is 32 atm and 40% of CO has reacted. Write the expression for the equilibrium constant, Kp, for this reaction. Use your expression to calculate the value of Kp for this reaction. Include its units.