The decomposition reaction occurs at 298 K

CHEMISTRY · Single correct · A Level · Chemistry · Thermodynamics · Thermodynamics

Problem

The decomposition reaction

\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

\Delta S^\circ_{\text{rxn}}

for this process and provides the best justification? (a)

\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)

\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)

\Delta S^\circ_{\text{rxn}}

is negative because breaking the N–N bond in

\text{N}_2\text{O}_4

lowers the randomness of the molecules. (d)

\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.