Nitric oxide and oxygen react to form nitrogen dioxide according to the balanced…

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

Problem

Nitric oxide and oxygen react to form nitrogen dioxide according to the balanced equation 2 NO(g)+O2(g)→2 NO2(g)ΔH∘=−114 kJ2\,\text{NO(g)} + \text{O}_2\text{(g)} \rightarrow 2\,\text{NO}_2\text{(g)} \quad \Delta H^\circ = -114\,\text{kJ} (for the reaction as written) The standard molar enthalpies of formation that are relevant to this reaction (at 298 K) are: • NO(g): 90.3 kJ mol−190.3\,\text{kJ}\,\text{mol}^{-1} • O2_2(g): 0 kJ mol−10\,\text{kJ}\,\text{mol}^{-1} (by convention) Answer the following. (1) Part 1: Calculate the standard molar enthalpy of formation, ΔHx∘\Delta H^\circ_x, for NO2(g)\text{NO}_2\text{(g)} in kJ mol−1\text{kJ}\,\text{mol}^{-1}. Show all work, including appropriate unit analysis. (2) Part 2: Explain, with reference to the sign and magnitude of your calculated value, whether the formation of NO2(g)\text{NO}_2\text{(g)} from its constituent elements is exothermic or endothermic under standard conditions.

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