Dinitrogen tetroxide,

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

Problem

Dinitrogen tetroxide, N2O4(g)N_2O_4(g), is in equilibrium with nitrogen dioxide, 2 NO2(g)2\,NO_2(g), at 1 bar pressure. For this reaction, the standard enthalpy change is ΔH∘=+57.2 kJ mol−1\Delta H^\circ = +57.2\,\text{kJ mol}^{-1} and the standard entropy change is ΔS∘=+175 J mol−1 K−1\Delta S^\circ = +175\,\text{J mol}^{-1}\,\text{K}^{-1}. Answer the following questions about how temperature affects the position of equilibrium for this system. (a) Qualitatively determine the sign of the standard Gibbs free-energy change ΔG∘\Delta G^\circ at 298 K298\,\text{K} without performing a numerical calculation. Explain your reasoning in terms of the magnitudes of ΔH∘\Delta H^\circ and TΔS∘T\Delta S^\circ. (b) Based on your answer to part (a), predict whether the equilibrium constant KK at 298 K298\,\text{K} is greater than 1, equal to 1, or less than 1. Justify your prediction. (c) Describe how the value of KK is expected to change as temperature increases well above 298 K298\,\text{K}. Explain your reasoning in terms of thermodynamics for this specific reaction.

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