Chemistry 9701 · AS & A Level · Nitrogen and sulfur

Nitrogen and sulfur — practice question

Sulfur trioxide, $\text{SO}_3$, is made from sulfur dioxide and oxygen in the Contact process. $\text{2SO}_2(\text{g}) + \text{O}_2(\text{g}) \rightleftharpoons \text{2SO}_3(\text{g}) \;\; \Delta H = -196.0\ \text{kJ mol}^{-1}$.
(a(i))[2]

Define what is meant by enthalpy change of formation.

(a(ii))[2]

Use the data to calculate the enthalpy change of formation of $\text{SO}_3(\text{g})$.

(b(i))[1]

The Boltzmann distribution for a mixture of $\text{SO}_2$ and $\text{O}_2$ at $700\ \text{K}$ is shown. $E_{a\,\text{cat}}$ shows the activation energy when the catalyst is present. Add a labelled mark, $E_{a\,\text{uncat}}$, to the diagram to indicate the activation energy when the catalyst is absent.

(b(ii))[2]

State the benefit of using a catalyst in this reaction. Explain how it brings about this effect.

(b(iii))[4]

State and explain how an increase in pressure would affect both the rate of reaction and the yield of $\text{SO}_3$ in the Contact process.

(ii)[2]

State the benefit of using a catalyst in this reaction. Explain how it brings about this effect.

(iii)[4]

State and explain how an increase in pressure would affect both the rate of reaction and the yield of $\text{SO}_3$ in the Contact process.

(c(i))[1]

At a pressure of $1.50 \times 10^5\,\text{Pa}$, $1.00\,\text{mol}$ of sulfur dioxide gas, $\text{SO}_2$, was mixed with $1.00\,\text{mol}$ of oxygen gas, $\text{O}_2$. The equilibrium mixture formed was found to contain $0.505\,\text{mol}$ of $\text{O}_2$. The equilibrium is: $\text{2SO}_2(g) + \text{O}_2(g) \rightleftharpoons \text{2SO}_3(g)$ Calculate the amount, in mol, of $\text{SO}_2$ and $\text{SO}_3$ in the equilibrium mixture.

(c(ii))[2]

Calculate the partial pressure of oxygen gas, $p_{\text{O}_2}$, in the equilibrium mixture.

(d(i))[1]

For another equilibrium mixture made from different starting amounts of $\text{SO}_2$ and $\text{O}_2$, the partial pressures were: $p_{\text{SO}_2} = 8.42 \times 10^2\,\text{Pa}$ $p_{\text{O}_2} = 6.00 \times 10^4\,\text{Pa}$ $p_{\text{SO}_3} = 9.10 \times 10^4\,\text{Pa}$ Write the expression for the equilibrium constant, $K_p$, for the formation of $\text{SO}_3$ from $\text{SO}_2$ and $\text{O}_2$.

(d(ii))[2]

Calculate the value of $K_p$ for this reaction and state the units.

Worked solution & mark scheme

This 23-mark question has a full step-by-step worked solution and mark scheme. One marking point: Enthalpy / energy change for the formation of one mole of a compound

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI