Hydrogenation of propene produces propane. Calculate the standard entropy change, ΔS^θ, for the hydrogenation of propene.

The standard enthalpy change, ΔH ^θ, for the hydrogenation of propene is –124.4 kJ mol^–1. Predict the temperature above which the hydrogenation reaction is not spontaneous.

«ΔS^θ =» 270 «J K^–1 mol^–1» – 267 «J K^–1 mol^–1» – 131 «J K^–1 mol^–1»

«ΔS^θ =» –128 «J K^–1 mol^–1»

Award [2] for correct final answer.

[2 marks]

«non spontaneous if» ΔG ^θ = ΔH ^θ – TΔS ^θ > 0
OR
ΔH ^θ > TΔS ^θ

«T above» \(\frac{{ - 124.4{\text{ }}\ll {\text{kJ}}\,{\text{mo}}{{\text{l}}^{ - {\text{1}}}}\gg }}{{ - 0.128{\text{ }}\ll {\text{kJ}}\,{{\text{K}}^{ - 1}}\,{\text{mo}}{{\text{l}}^{ - {\text{1}}}}\gg }} = \)» 972 «K»

Award [2] for correct final answer.

Accept 699 °C.

Do not award M2 for any negative T value.

[2 marks]