Cambridge International A Level · Chemistry (9701)
5 multiple-choice questions marked as you go, and 4 written questions with worked solutions. All on Equilibria (AS).
For the reversible reaction \( \text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \), what happens if the concentration of \( \text{H}_2\text{(g)} \) is increased at constant temperature and pressure?
Consider the reaction: \( \text{2SO}_2\text{(g)} + \text{O}_2\text{(g)} \rightleftharpoons \text{2SO}_3\text{(g)} \quad \Delta H = -197 \text{ kJ mol}^{-1} \).
Which of the following changes will increase the equilibrium yield of \( \text{SO}_3 \)?
The partition coefficient, \( K_{pc} \), of a solute \( X \) between hexane and water is 8.0.
\( K_{pc} = \frac{[X]_{\text{hexane}}}{[X]_{\text{water}}} = 8.0 \)
An aqueous solution contains \( 10.0 \text{ g} \) of \( X \) in \( 100 \text{ cm}^3 \) of water. This solution is shaken with two successive \( 20 \text{ cm}^3 \) portions of hexane. What is the total mass of \( X \) extracted into the hexane layers?
For the reaction \( \text{H}_2\text{(g)} + \text{I}_2\text{(g)} \rightleftharpoons \text{2HI(g)} \), at a certain temperature, 1.0 mol of \( \text{H}_2 \) and 1.0 mol of \( \text{I}_2 \) are placed in a 2.0 dm³ container. At equilibrium, 0.4 mol of \( \text{HI} \) is formed. Calculate the value of \( K_c \).
For the decomposition of dinitrogen tetroxide: \( \text{N}_2\text{O}_4\text{(g)} \rightleftharpoons \text{2NO}_2\text{(g)} \).
At \( 25^\circ\text{C} \), \( K_p = 0.11 \text{ atm} \). At \( 100^\circ\text{C} \), \( K_p = 11 \text{ atm} \).
Which statement about this reaction is correct?
For the reversible reaction:
\(2\mathrm{SO}_2(\mathrm{g}) + \mathrm{O}_2(\mathrm{g}) \rightleftharpoons 2\mathrm{SO}_3(\mathrm{g}) \quad \Delta H = -197 \mathrm{\,kJ\,mol}^{-1}\)
Predict and explain the effect on the position of equilibrium when the pressure is increased.
Write your answer out first, then check it against the worked solution.
Explain why a catalyst does not affect the position of equilibrium for a reversible reaction, despite increasing the rate of reaction.
Write your answer out first, then check it against the worked solution.
(a) Define pH.
(b) Calculate the pH of a \( 0.020 \text{ mol dm}^{-3} \) solution of hydrochloric acid, \( \text{HCl} \).
(c) Ethanoic acid, \( \text{CH}_3\text{COOH} \), is a weak acid with an acid dissociation constant, \( K_a \), of \( 1.74 \times 10^{-5} \text{ mol dm}^{-3} \) at \( 298 \text{ K} \). Calculate the pH of a \( 0.10 \text{ mol dm}^{-3} \) solution of ethanoic acid.
Write your answer out first, then check it against the worked solution.
The reversible reaction between nitrogen and hydrogen to form ammonia is an important industrial process, the Haber process:
\( \text{N}_2\text{(g)} + 3\text{H}_2\text{(g)} \rightleftharpoons 2\text{NH}_3\text{(g)} \quad \Delta H = -92 \text{ kJ mol}^{-1} \)
(a) Explain how a catalyst affects the rate of this reaction and the position of equilibrium.
(b) A mixture of \( 2.0 \text{ mol} \) of \( \text{N}_2 \) and \( 6.0 \text{ mol} \) of \( \text{H}_2 \) is placed in a \( 1.0 \text{ dm}^3 \) container. At equilibrium, \( 3.0 \text{ mol} \) of \( \text{NH}_3 \) are present.
(i) Calculate the number of moles of \( \text{N}_2 \) and \( \text{H}_2 \) present at equilibrium.
(ii) Write the expression for \( K_c \) for this reaction.
(iii) Calculate the value of \( K_c \) at this temperature, stating its units.
Write your answer out first, then check it against the worked solution.
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