Chemistry

Chemistry

Problem

A chemistry research group measured the standard entropy change, ΔS∘\Delta S^\circ, for four independent processes at 298 K. The data are summarized in the table below.
Process (298 K)ΔS∘\Delta S^\circ (J mol−1^{-1} K−1^{-1})
I. C (s)+O2 (g)→CO2 (g)\text{C\,(s)} + \text{O}_2\,(g) \rightarrow \text{CO}_2\,(g)–173
II. H2 (g)+12 O2 (g)→H2O (l)\text{H}_2\,(g) + \tfrac12\,\text{O}_2\,(g) \rightarrow \text{H}_2\text{O}\,(l)–163
III. N2 (g)+3 H2 (g)→2 NH3 (g)\text{N}_2\,(g) + 3\,\text{H}_2\,(g) \rightarrow 2\,\text{NH}_3\,(g)–198
IV. CaCO3 (s)→CaO (s)+CO2 (g)\text{CaCO}_3\,(s) \rightarrow \text{CaO}\,(s) + \text{CO}_2\,(g)+161
(a) Rank the four processes from the one that produces the greatest increase in system disorder to the one that produces the greatest decrease in system disorder. Justify your ranking using only the numerical data provided. (b) For process II, explain in terms of molecular-level changes why ΔS∘\Delta S^\circ is negative even though only one mole of liquid water is produced from gaseous reactants. (c) A student claims that process IV must be spontaneous at 298 K because its ΔS∘\Delta S^\circ value is positive. Evaluate the validity of the claim, citing at least two factors that determine spontaneity.

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