Chemistry 9701 · AS & A Level · Chemical energetics

Chemical energetics — practice question

Nitric acid is produced industrially by oxidising ammonia. The overall equation for this process is shown below. Equation 1: $\text{NH}_3 + 2\text{O}_2 \rightarrow \text{HNO}_3 + \text{H}_2\text{O}$. This process takes place in three stages. The equations and enthalpy changes for each stage are given. Stage 1: $4\text{NH}_3 + 5\text{O}_2 \rightarrow 4\text{NO} + 6\text{H}_2\text{O}$, $\Delta H = -904~\text{kJ mol}^{-1}$. Stage 2: $2\text{NO} + \text{O}_2 \rightarrow 2\text{NO}_2$, $\Delta H = -114~\text{kJ mol}^{-1}$. Stage 3: $4\text{NO}_2 + \text{O}_2 + 2\text{H}_2\text{O} \rightarrow 4\text{HNO}_3$, $\Delta H = -348~\text{kJ mol}^{-1}$. What is the enthalpy change for the process shown in equation 1?

  • A$-1480~ ext{kJ mol}^{-1}$
  • B$-370~ ext{kJ mol}^{-1}$
  • C$-341.5~ ext{kJ mol}^{-1}$
  • D$+82~ ext{kJ mol}^{-1}$

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