Consider the combustion of methane carried out in two different ways

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

Problem

Consider the combustion of methane carried out in two different ways. Reaction A: CH4 (g)+2 O2 (g)→CO2 (g)+2 H2O (l)\text{CH}_4\,(g) + 2\,\text{O}_2\,(g) \rightarrow \text{CO}_2\,(g) + 2\,\text{H}_2\text{O}\,(l) Reaction B: CH4 (g)+2 O2 (g)→CO2 (g)+2 H2O (g)\text{CH}_4\,(g) + 2\,\text{O}_2\,(g) \rightarrow \text{CO}_2\,(g) + 2\,\text{H}_2\text{O}\,(g) Absolute molar entropies at 298 K are provided.
SubstanceS∘S^\circ (J mol−1^{-1} K−1^{-1})
CH4 (g)\text{CH}_4\,(g)186
O2 (g)\text{O}_2\,(g)205
CO2 (g)\text{CO}_2\,(g)214
H2O (l)\text{H}_2\text{O}\,(l)70
H2O (g)\text{H}_2\text{O}\,(g)189
(a) Calculate ΔS298∘\Delta S^\circ_{298} for Reaction A. (b) Calculate ΔS298∘\Delta S^\circ_{298} for Reaction B. (c) Quantitatively determine by how much (in J mol−1^{-1} K−1^{-1}) the entropy change differs between the two reactions and account for the difference in terms of the physical states of the products. (d) Discuss how the sign and magnitude of ΔS∘\Delta S^\circ for Reaction A could influence the minimum temperature required for the combustion to be thermodynamically favorable.

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