At 298 K the decomposition of calcium carbonate is thermodynamically unfavorable:

CHEMISTRY · Single correct · AP · Chemistry · Thermodynamics and Electrochemistry · Thermodynamics and Electrochemistry

Problem

At 298 K the decomposition of calcium carbonate is thermodynamically unfavorable: CaCO3(s)→CaO(s)+CO2(g)ΔG∘=+178 kJ mol−1\text{CaCO}_3(s) \rightarrow \text{CaO}(s)+\text{CO}_2(g) \quad \Delta G^{\circ}=+178\,\text{kJ mol}^{-1}. Which of the following exergonic reactions could be coupled to this decomposition so that the shared species cancels and the overall process becomes favorable? (a) CaO(s)+SO2(g)→CaSO3(s)ΔG∘=−230 kJ mol−1\text{CaO}(s)+\text{SO}_2(g) \rightarrow \text{CaSO}_3(s)\qquad \Delta G^{\circ}=-230\,\text{kJ mol}^{-1} (b) CaO(s)+H2O(l)→Ca(OH)2(s)ΔG∘=−64 kJ mol−1\text{CaO}(s)+\text{H}_2\text{O}(l) \rightarrow \text{Ca(OH)}_2(s)\qquad \Delta G^{\circ}=-64\,\text{kJ mol}^{-1} (c) 12O2(g)+H2(g)→H2O(l)ΔG∘=−237 kJ mol−1\tfrac12\text{O}_2(g)+\text{H}_2(g) \rightarrow \text{H}_2\text{O}(l)\qquad \Delta G^{\circ}=-237\,\text{kJ mol}^{-1} (d) CaSO3(s)→CaO(s)+SO2(g)ΔG∘=−230 kJ mol−1\text{CaSO}_3(s) \rightarrow \text{CaO}(s)+\text{SO}_2(g)\qquad \Delta G^{\circ}=-230\,\text{kJ mol}^{-1}

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