Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Ammonia, $\text{NH}_3$, is produced from nitrogen and hydrogen in the Haber process. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$  $\Delta H = -92\ \text{kJ mol}^{-1}$
(a(i))[2]

Explain what is meant by the term bond energy.

(a(ii))[2]

Use the data to work out the N-H bond energy. Show all steps in your working.

(b(i))[2]

On the same axes, draw a second curve to show the Boltzmann distribution at a higher temperature.

(b(ii))[3]

Using the Boltzmann distribution, state and explain how increasing temperature affects the rate of ammonia production.

(b(iii))[3]

State and explain how increasing temperature affects the yield of ammonia. Use Le Chatelier’s principle in your answer.

(c(i))[2]

Calculate the amounts, in mol, of $\text{N}_2(g)$ and $\text{H}_2(g)$ in the equilibrium mixture, given that at a pressure of $2.00 \times 10^7\ \text{Pa}$, $1.00\ \text{mol}$ of $\text{N}_2(g)$ was mixed with $3.00\ \text{mol}$ of $\text{H}_2(g)$ and the final equilibrium mixture contained $0.300\ \text{mol}$ of $\text{NH}_3(g)$.

(c(ii))[3]

Calculate the partial pressure of ammonia, $p\text{NH}_3$, in the equilibrium mixture. Give your answer to three significant figures.

(d(i))[1]

Write the expression for the equilibrium constant, $K_p$, for the production of ammonia from nitrogen and hydrogen.

(d(ii))[2]

Calculate the value of $K_p$ for this reaction. State the units.

(d(iii))[2]

The reaction is repeated with the same starting amounts of nitrogen and hydrogen. The temperature stays the same, but the container volume is smaller. State the effects, if any, of this change on the yield of ammonia and on the value of $K_p$.

Worked solution & mark scheme

This 22-mark question has a full step-by-step worked solution and mark scheme. One marking point: Energy needed / required to break 1 mole of (covalent) bonds

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