Nitric oxide reacts with dioxygen to form nitrogen dioxide

CHEMISTRY · Multi-part · A Level · Chemistry · Energetics · Energetics

Problem

Nitric oxide reacts with dioxygen to form nitrogen dioxide, which can further dimerize to dinitrogen tetroxide under certain conditions. Step 1 Formation of NO2\mathrm{NO_2} 2 NO(g)+O2(g)⟶2 NO2(g)ΔH1=−114  kJ mol−1\mathrm{2\,NO(g)+O_2(g)\longrightarrow 2\,NO_2(g)} \qquad \Delta H_1 = -114\;\text{kJ\,mol}^{-1} (per mole of reaction as written) Step 2 Dimerization of NO2\mathrm{NO_2} 2 NO2(g)⟶N2O4(g)ΔH2=−58  kJ mol−1\mathrm{2\,NO_2(g)\longrightarrow N_2O_4(g)} \qquad \Delta H_2 = -58\;\text{kJ\,mol}^{-1} (per mole of reaction as written) A sealed, rigid vessel at constant pressure initially contains 0.400 mol0.400\,\text{mol} of NO(g)\mathrm{NO(g)} and 0.200 mol0.200\,\text{mol} of O2(g)\mathrm{O_2(g)} at 298 K298\,\text{K}. The reactions occur sequentially as follows: 1. All available NO\mathrm{NO} and O2\mathrm{O_2} react completely according to Step 1. 2. Exactly 30.0%30.0\% of the NO2\mathrm{NO_2} produced in Step 1 subsequently dimerizes according to Step 2. The remainder stays as NO2(g)\mathrm{NO_2(g)}. Answer the questions below. (a) Identify the limiting reagent in Step 1 and calculate the moles of NO2\mathrm{NO_2} formed in that step. (b) Determine the heat released in Step 1. (c) Calculate the moles of N2O4\mathrm{N_2O_4} produced in Step 2 and the additional heat released in this step. (d) Compute the total heat released by Steps 1 and 2 combined. (e) List the final amounts (in moles) of NO2\mathrm{NO_2}, N2O4\mathrm{N_2O_4}, and any excess O2\mathrm{O_2} remaining in the vessel.

Related theory

Browse the problem library