(a)

Consider the following two equilibria and associated data values at 298 K .

\begin{array}{ccc} \mathrm{AgBr}(\mathrm{~s}) \rightleftharpoons \mathrm{Ag}^{+}(\mathrm{aq})+\mathrm{Br}^{-}(\mathrm{aq}) & \text { equilibrium } 1 \quad K_{\mathrm{sp}}=5.0 \times 10^{-13} \mathrm{~mol}^{2} \mathrm{dm}^{-6} \\ \mathrm{Ag}^{+}(\mathrm{aq})+2 \mathrm{NH}_{3}(\mathrm{aq}) \rightleftharpoons\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}(\mathrm{aq}) & \text { equilibrium } 2 \quad K_{\text {stab }}=1.7 \times 10^{7} \mathrm{~mol}^{-2} \mathrm{dm}^{6} \end{array}

The equilibrium constant for equilibrium 1 is the solubility product, $K_{\mathrm{sp}}$ , of AgBr(s). The equilibrium constant for equilibrium 2 is the stability constant, $K_{\text {stab }}$ , for the formation of $\left[\mathrm{Ag}\left(\mathrm{NH}_{3}\right)_{2}\right]^{+}(\mathrm{aq})$ .

[ 2 ]

(i)

Use Le Chatelier's principle as applied to equilibria 1 and 2 to suggest why $\operatorname{AgBr}(\mathbf{s})$ dissolves in concentrated $\mathrm{NH}_{3}(\mathrm{aq})$ .

[ 2 ]

[Maximum number: 11]

The elements sodium to chlorine, in the third period, all form oxides.

(a)

$\mathrm{SO}_{3}$ is produced by the reaction between $\mathrm{SO}_{2}$ and $\mathrm{O}_{2}$ in the Contact process. A dynamic equilibrium is established.

2 \mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{SO}_{3}(\mathrm{~g}) \quad \Delta H=-196 \mathrm{~kJ} \mathrm{~mol}^{-1}

[ 5 ]

(i)

Explain why increasing the total pressure, at constant temperature, increases the rate of production of $\mathrm{SO}_{3}$ and increases the yield of $\mathrm{SO}_{3}$ .
rate
yield

The graph shows how the concentrations of all three species in the system change with time for a typical reaction mixture. The gradients of all three lines decrease with time and then level off in this dynamic equilibrium.

[ 4 ]

(ii)

Explain why all three lines become horizontal.

[ 1 ]

(b)

2.00 moles of $\mathrm{SO}_{2}(\mathrm{~g})$ and 2.00 moles of $\mathrm{O}_{2}(\mathrm{~g})$ are sealed in a container with a suitable catalyst, at constant temperature and pressure. The resulting equilibrium mixture contains 1.98 moles of $\mathrm{SO}_{3}(\mathrm{~g})$ .
The total volume of the equilibrium mixture is $40.0 \mathrm{dm}^{3}$ .

2 \mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{SO}_{3}(\mathrm{~g})

[ 6 ]

(i)

Write the expression for the equilibrium constant, $K_{\mathrm{c}}$ , for the reaction between $\mathrm{SO}_{2}(\mathrm{~g})$ and $\mathrm{O}_{2}(\mathrm{~g})$ to produce $\mathrm{SO}_{3}(\mathrm{~g})$ .

K_{c}=

[ 1 ]

(ii)

Calculate the amount, in moles, of $\mathrm{SO}_{2}(\mathrm{~g})$ and $\mathrm{O}_{2}(\mathrm{~g})$ in the equilibrium mixture.

\begin{array}{r} \mathrm{SO}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{mol} \\ \mathrm{O}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \mathrm{mol} \end{array}

[ 2 ]

(iii)

Use your answers to (d)(i) and (d)(ii) to calculate the value of $K_{\mathrm{c}}$ for this equilibrium mixture. Give the units of $K_{\mathrm{c}}$ .

\begin{array}{r} K_{\mathrm{c}}= \\ \text { units }= \end{array}

[ 3 ]

[Maximum number: 3]

Sulfuric acid is manufactured by the Contact process.
One stage in this process is the conversion of sulfur dioxide into sulfur trioxide in the presence of a heterogeneous catalyst of vanadium(V) oxide, $\mathrm{V}_{2} \mathrm{O}_{5}$ .

(a)

(i)

State and explain the effect of increasing temperature on the yield of $\mathrm{SO}_{3}$ .

[ 3 ]

[Maximum number: 10]

Ammonia, $\mathrm{NH}_{3}$ , is manufactured from nitrogen and hydrogen by the Haber process.

\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-92 \mathrm{~kJ} \mathrm{~mol}^{-1}

(a)

The Haber process is usually carried out at a temperature of approximately $400^{\circ} \mathrm{C}$ in the presence of a catalyst. Changing the temperature affects both the rate of production of ammonia and the yield of ammonia.

The Boltzmann distribution for a mixture of nitrogen and hydrogen at $400^{\circ} \mathrm{C}$ is shown. Ea represents the activation energy for the reaction.

[ 3 ]

(i)

State and explain the effect of increasing temperature on the yield of ammonia. Use Le Chatelier's principle to explain your answer.

[ 3 ]

(b)

At a pressure of $2.00 \times 10^{7} \mathrm{~Pa}, 1.00 \mathrm{~mol}$ of nitrogen, $\mathrm{N}_{2}(\mathrm{~g})$ , was mixed with 3.00 mol of hydrogen, $\mathrm{H}_{2}(\mathrm{~g})$ . The final equilibrium mixture formed contained 0.300 mol of ammonia, $\mathrm{NH}_{3}(\mathrm{~g})$ .

[ 2 ]

(i)

Calculate the amounts, in mol, of $\mathrm{N}_{2}(\mathrm{~g})$ and $\mathrm{H}_{2}(\mathrm{~g})$ in the equilibrium mixture.

\begin{aligned} & \mathrm{N}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \text { mol } \\ & \mathrm{H}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \text { mol } \end{aligned}

[ 2 ]

(ii)

Calculate the partial pressure of ammonia, $\mathrm{pNH}_{3}$ , in the equilibrium mixture.

Give your answer to three significant figures.

p \mathrm{NH}_{3}=

Pa

(c)

In another equilibrium mixture the partial pressures are as shown.

[ 5 ]

(i)

Write the expression for the equilibrium constant, $K_{\mathrm{p}}$ , for the production of ammonia from nitrogen and hydrogen.

K_{p}=

[ 1 ]

(ii)

Calculate the value of $K_{\mathrm{p}}$ for this reaction.

State the units.

K_{p}=

units =

[ 2 ]

(iii)

This reaction is repeated with the same starting amounts of nitrogen and hydrogen. The same temperature is used but the container has a smaller volume.

State the effects, if any, of this change on the yield of ammonia and on the value of $K_{\mathrm{p}}$ . effect on yield of ammonia
effect on value of $K_{p}$

[ 2 ]

[Maximum number: 7]

Methylpropane, $\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{3}$ , is an isomer of butane, $\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}$ .

(a)

When a sample of butane is heated to 373 K , in the presence of a catalyst, and allowed to reach equilibrium the following reaction occurs.

\mathrm{CH}_{3}\left(\mathrm{CH}_{2}\right)_{2} \mathrm{CH}_{3}(\mathrm{~g}) \rightleftharpoons\left(\mathrm{CH}_{3}\right)_{2} \mathrm{CHCH}_{3}(\mathrm{~g}) \quad \Delta H=-8.0 \mathrm{~kJ} \mathrm{~mol}^{-1}

State and explain the effect on the composition of this equilibrium mixture when the temperature is increased to 473 K .

[ 2 ]

(b)

1 mole of butane gas was added to a $1 \mathrm{dm}^{3}$ closed system, at a constant temperature and pressure. The amount of butane and methylpropane was measured at regular time intervals.

[ 5 ]

(i)

Label the graph with a t to show the time taken to reach dynamic equilibrium.

[ 1 ]

(ii)

Use the graph to find the concentration of butane and methylpropane in the mixture at equilibrium.
concentration of butane = $\mathrm{mol} \mathrm{dm}^{-3}$
concentration of methylpropane = $\mathrm{mol} \mathrm{dm}^{-3}$

[ 1 ]

(iii)

Write an expression for $K_{\mathrm{c}}$ for this reaction.

[ 1 ]

(iv)

Calculate a value for $K_{\mathrm{c}}$ and state its units.

K_{\mathrm{c}}=

units =

[ 2 ]

[Maximum number: 4]

In the Periodic Table, the p block contains elements whose outer electrons are found in the p subshell.

(a)

$\mathrm{SO}_{2}$ can react with ozone, $\mathrm{O}_{3}$ , to form $\mathrm{SO}_{3}$ in two different reactions.

[ 4 ]

(i)

In one reaction, $\mathrm{SO}_{2}$ reacts with $\mathrm{O}_{3}$ until a dynamic equilibrium is established.

\mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{3}(\mathrm{~g}) \rightleftharpoons \mathrm{SO}_{3}(\mathrm{~g})+\mathrm{O}_{2}(\mathrm{~g})

State and explain the effect of an increase in pressure on the composition of the equilibrium mixture.

[ 2 ]

(ii)

In the other reaction, a different equilibrium is established at 300 K as shown.

3 \mathrm{SO}_{2}(\mathrm{~g})+\mathrm{O}_{3}(\mathrm{~g}) \rightleftharpoons 3 \mathrm{SO}_{3}(\mathrm{~g}) \quad \Delta H=+462.3 \mathrm{~kJ} \mathrm{~mol}^{-1}

Suggest a temperature needed to increase the yield of $\mathrm{SO}_{3}$ at equilibrium.
Explain your answer.

[ 2 ]

[Maximum number: 10]

Ammonia, $\mathrm{NH}_{3}$ , is manufactured from nitrogen and hydrogen by the Haber process.

\mathrm{N}_{2}(\mathrm{~g})+3 \mathrm{H}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{NH}_{3}(\mathrm{~g}) \quad \Delta H=-92 \mathrm{~kJ} \mathrm{~mol}^{-1}

(a)

The Haber process is usually carried out at a temperature of approximately $400^{\circ} \mathrm{C}$ in the presence of a catalyst. Changing the temperature affects both the rate of production of ammonia and the yield of ammonia.

The Boltzmann distribution for a mixture of nitrogen and hydrogen at $400^{\circ} \mathrm{C}$ is shown. Ea represents the activation energy for the reaction.

[ 3 ]

(i)

State and explain the effect of increasing temperature on the yield of ammonia. Use Le Chatelier's principle to explain your answer.

[ 3 ]

(b)

At a pressure of $2.00 \times 10^{7} \mathrm{~Pa}, 1.00 \mathrm{~mol}$ of nitrogen, $\mathrm{N}_{2}(\mathrm{~g})$ , was mixed with 3.00 mol of hydrogen, $\mathrm{H}_{2}(\mathrm{~g})$ . The final equilibrium mixture formed contained 0.300 mol of ammonia, $\mathrm{NH}_{3}(\mathrm{~g})$ .

[ 2 ]

(i)

Calculate the amounts, in mol, of $\mathrm{N}_{2}(\mathrm{~g})$ and $\mathrm{H}_{2}(\mathrm{~g})$ in the equilibrium mixture.

\begin{aligned} & \mathrm{N}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . \text { mol } \\ & \mathrm{H}_{2}(\mathrm{~g})=\ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots \ldots . . \text { mol } \end{aligned}

[ 2 ]

(ii)

Calculate the partial pressure of ammonia, $\mathrm{pNH}_{3}$ , in the equilibrium mixture.

Give your answer to three significant figures.

p \mathrm{NH}_{3}=

Pa

(c)

In another equilibrium mixture the partial pressures are as shown.

[ 5 ]

(i)

Write the expression for the equilibrium constant, $K_{\mathrm{p}}$ , for the production of ammonia from nitrogen and hydrogen.

K_{p}=

[ 1 ]

(ii)

Calculate the value of $K_{p}$ for this reaction.

State the units.

K_{p}=

units =

[ 2 ]

(iii)

This reaction is repeated with the same starting amounts of nitrogen and hydrogen. The same temperature is used but the container has a smaller volume.

State the effects, if any, of this change on the yield of ammonia and on the value of $K_{\mathrm{p}}$ . effect on yield of ammonia
effect on value of $K_{p}$

[ 2 ]

[Maximum number: 10]

Ethanoic acid can be reacted with alcohols to form esters, an equilibrium mixture being formed.

\mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{H}+\mathrm{ROH} \rightleftharpoons \mathrm{CH}_{3} \mathrm{CO}_{2} \mathrm{R}+\mathrm{H}_{2} \mathrm{O}

The reaction is usually carried out in the presence of an acid catalyst.

(a)

Write an expression for the equilibrium constant, $K_{\mathrm{c}}$ , for this reaction, clearly stating the units.

K_{\mathrm{c}}=

units

In an experiment to determine $K_{\mathrm{c}}$ a student placed together in a conical flask 0.10 mol of ethanoic acid, 0.10 mol of an alcohol ROH, and 0.005 mol of hydrogen chloride catalyst.
The flask was sealed and kept at $25^{\circ} \mathrm{C}$ for seven days.
After this time, the student titrated all of the contents of the flask with $2.00 \mathrm{moldm}^{-3} \mathrm{NaOH}$ using phenolphthalein indicator.
At the end-point, $22.5 \mathrm{~cm}^{3}$ of NaOH had been used.

[ 2 ]

(b)

(i)

Use your results from (b) to calculate the amount, in moles, of ethanoic acid present at equilibrium. Hence complete the table below.

[ 3 ]

(ii)

Use your results to calculate a value for $K_{\mathrm{c}}$ for this reaction.

[ 3 ]

(c)

What would be the effect, if any, on the amount of ester present if all of the water were removed from the flask and the flask kept for a further week at $25^{\circ} \mathrm{C}$ ?

Explain your answer.

[ 2 ]

(a)

When concentrated hydrochloric acid is added to a solution containing $\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}$ , a blue solution of $\left[\mathrm{CoCl}_{4}\right]^{2-}$ is formed and the following equilibrium is established.

\left[\mathrm{Co}\left(\mathrm{H}_{2} \mathrm{O}\right)_{6}\right]^{2+}+4 \mathrm{Cl}^{-} \rightleftharpoons\left[\mathrm{CoCl}_{4}\right]^{2-}+6 \mathrm{H}_{2} \mathrm{O}

Use Le Chatelier's principle to suggest the expected observations when silver nitrate solution is added dropwise to the blue solution of $\left[\mathrm{CoCl}_{4}\right]^{2-}$ . Explain your answer.

[ 2 ]

[Maximum number: 4]

Hydrogen iodide, HI, is a colourless gas at room temperature.

(a)

HI(g) can be formed by reacting $\mathrm{H}_{2}(\mathrm{~g})$ with $\mathrm{I}_{2}(\mathrm{~g})$ . The reaction is reversible, and an equilibrium forms quickly at high temperatures.

\mathrm{H}_{2}(\mathrm{~g})+\mathrm{I}_{2}(\mathrm{~g}) \rightleftharpoons 2 \mathrm{HI}(\mathrm{~g})

[ 4 ]

(i)

Construct an expression for the equilibrium constant, $K_{\mathrm{p}}$ , for the reaction of $\mathrm{H}_{2}(\mathrm{~g})$ and $\mathrm{I}_{2}(\mathrm{~g})$ to form HI(g).

K_{\mathrm{p}}=

[ 1 ]

(ii)

The equilibrium partial pressures of the gases at $200^{\circ} \mathrm{C}$ are as follows.

\begin{aligned} & p_{\mathrm{H}_{2}(\mathrm{~g})}=895 \mathrm{~Pa} \\ & p_{\mathrm{I}_{2}(\mathrm{~g})}=895 \mathrm{~Pa} \\ & p_{\mathrm{HI}(\mathrm{~g})}=4800 \mathrm{~Pa} \end{aligned}

Calculate $K_{p}$ for this reaction.

K_{\mathrm{p}}=

[ 1 ]

(iii)

State how the value of $K_{\mathrm{p}}$ would change, if at all, if the reaction were carried out at $100^{\circ} \mathrm{C}$ rather than $200^{\circ} \mathrm{C}$ .

Explain your answer.

[ 2 ]

Question 1

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