Chemistry

Chemistry

Problem

The decomposition reaction N2O4(g)→2 NO2(g)\text{N}_2\text{O}_4(g) \rightarrow 2\,\text{NO}_2(g) occurs at 298 K. Which statement most accurately predicts the sign of ΔSrxn∘\Delta S^\circ_{\text{rxn}} for this process and provides the best justification? a) ΔSrxn∘\Delta S^\circ_{\text{rxn}} is positive because the reaction is endothermic at 298\,\text{K}, and endothermic processes always increase the disorder of a system. b) ΔSrxn∘\Delta S^\circ_{\text{rxn}} is positive because two moles of gaseous product are formed from one mole of gaseous reactant, increasing the number of microstates available. c) ΔSrxn∘\Delta S^\circ_{\text{rxn}} is negative because breaking the N–N bond in N2O4\text{N}_2\text{O}_4 lowers the randomness of the molecules. d) ΔSrxn∘\Delta S^\circ_{\text{rxn}} is negative because producing additional gas molecules raises the pressure in a closed container, and higher pressure corresponds to lower entropy.
Intuitive explanation

This problem tests whether you can predict entropy change by counting particles and thinking about molecular disorder. The key insight is that decomposition reactions that produce more gas molecules from fewer gas molecules always increase disorder—you're going from one container of gas to effectively two containers' worth of molecular chaos. Count the moles of gas on each side, then reason about what happens to the system's randomness when molecules have more space and freedom to move around.

Intuitive explanation

This problem tests whether you can predict entropy change by counting particles and thinking about molecular disorder. The key insight is that decomposition reactions that produce more gas molecules from fewer gas molecules always increase disorder—you're going from one container of gas to effectively two containers' worth of molecular chaos. Count the moles of gas on each side, then reason about what happens to the system's randomness when molecules have more space and freedom to move around.

Browse the problem library