Equilibria

When an organic acid reacts with an alcohol, a reversible reaction takes place producing an ester and water.

$0.40\text{ mol}$ of an organic acid and $0.30\text{ mol}$ of an alcohol are mixed and allowed to stand at $25^\circ\text{C}$ until equilibrium is reached.

At equilibrium, $0.20\text{ mol}$ of ester is produced.

What is the value of the equilibrium constant, $K_{\text{c}}$, under the conditions used?

Options

A   0.33
B   0.50
C   2.0
D   10

Methanol is manufactured by reacting carbon dioxide and hydrogen together.

$$\text{CO}_2(\text{g}) + 3\text{H}_2(\text{g}) \rightleftharpoons \text{CH}_3\text{OH}(\text{g}) + \text{H}_2\text{O}(\text{g}) \quad \Delta H = -49\text{ kJ mol}^{-1}$$

What increases the equilibrium yield of methanol in this process?

Options

A   increasing the pressure
B   adding an excess of steam
C   adding a catalyst
D   increasing the temperature

An aqueous solution X contains substance HQ which behaves as a weak acid.

$$ext{HQ}(\text{aq}) \rightleftharpoons \text{H}^+(\text{aq}) + \text{Q}^-(\text{aq})$$

The soluble salt NaQ is added to X.

What happens to the $[\text{H}^+(\text{aq})]$ and the pH in X?

Options

Dinitrogen tetroxide, $\text{N}_2\text{O}_4$, decomposes reversibly.

$$\text{N}_2\text{O}_4 \rightleftharpoons 2\text{NO}_2 \quad \Delta H = +58.0 \text{ kJ mol}^{-1}$$

An equilibrium mixture of $\text{N}_2\text{O}_4$ and $\text{NO}_2$ gases is placed in a closed container under standard conditions.

$$K_c = 1.15 \times 10^{-1} \text{ mol dm}^{-3}$$

The conditions are changed.

Under the new conditions, $K_c = 1.70 \times 10^3 \text{ mol dm}^{-3}$.

Which change in conditions occurs?

Options

A   The pressure increases.
B   The pressure decreases.
C   The temperature increases.
D   The temperature decreases.

A reaction involving ammonium ions is shown.

$$\text{NH}_4^+ + \text{OH}^- \rightleftharpoons \text{NH}_3 + \text{H}_2\text{O}$$

Four statements about this reaction are listed.

1. The ammonium ions are reduced.
2. In the reverse reaction, ammonia acts as a Brønsted–Lowry base.
3. The ammonium ion and the ammonia molecule have the same bond angle.
4. This reaction is not a redox reaction.

Which statements are correct?

Options

A   1 and 2
B   1 and 3
C   2 and 4
D   3 and 4

The reaction between sulfur dioxide and oxygen has the equation shown.

$$2\text{SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons 2\text{SO}_3(\text{g}) \quad \Delta H = -197 \text{ kJ mol}^{-1}$$

$1.0\text{ mol}$ of $\text{SO}_2$ and $1.0\text{ mol}$ of $\text{O}_2$ are placed in a closed container and heated to a constant temperature.

At this temperature, $0.8\text{ mol}$ of $\text{SO}_3$ are present in the equilibrium mixture.

Which statement is correct?

Options

A   The equilibrium partial pressure of $\text{SO}_2$ is greater than the equilibrium partial pressure of $\text{O}_2$.
B   $K_p$ has units of $\text{mol dm}^{-3}$.
C   At a lower temperature, the equilibrium amount of $\text{SO}_3$ is lower than $0.8\text{ mol}$.
D   The mole fraction of $\text{SO}_3$ is less than 0.8.

In the Haber process, the reaction between the two gaseous reactants requires the use of a catalyst that contains a transition element.

What is the metal and in which mole ratio do the gases react?

Options

A reaction occurs when ammonium chloride is added to calcium hydroxide.

What is the role of the ammonium ions in this reaction?

Options

A   acid
B   base
C   oxidising agent
D   reducing agent

The equation shows the overall reaction between an amine and an acid chloride.

$$2\text{CH}_3\text{CH}_2\text{NH}_2 + \text{CH}_3\text{CH}_2\text{COCl} \rightarrow \text{CH}_3\text{CH}_2\text{CONHCH}_2\text{CH}_3 + \text{CH}_3\text{CH}_2\text{NH}_3\text{Cl}$$

The four steps in the mechanism are as follows.

Which steps are Brønsted–Lowry acid–base reactions?

Options

A   1 and 3
B   3 and 4
C   3 only
D   4 only

The reversible reaction shown is in equilibrium at a temperature of 450°C.

$$\text{H}_2 + \text{I}_2 \rightleftharpoons 2\text{HI} \quad \Delta H = -9.5\text{ kJ mol}^{-1}$$

The table shows the equilibrium concentrations in the reaction mixture.

The temperature of the reaction mixture is increased at constant volume.

The concentration of one of the components falls to $0.80\text{ mol dm}^{-3}$ at equilibrium under these conditions.

What is the concentration of $\text{H}_2$ in the new equilibrium mixture?

Options

A   $0.80\text{ mol dm}^{-3}$
B   $0.93\text{ mol dm}^{-3}$
C   $1.11\text{ mol dm}^{-3}$
D   $1.20\text{ mol dm}^{-3}$