Calcium carbonate decomposes according to the reaction below

CHEMISTRY · Multi-part · A Level · Chemistry · Chemical equilibria (Le Chatelier’s principle and Kc) · Chemical equilibria (Le Chatelier’s principle and Kc)

Problem

Calcium carbonate decomposes according to the reaction below, which is central to the industrial production of quicklime used in cement manufacturing. CaCO3(s)⇌CaO(s)+CO2(g)\mathrm{CaCO_3(s)} \rightleftharpoons \mathrm{CaO(s)} + \mathrm{CO_2(g)} Experimental measurements give the following values for the standard free-energy change: • ΔG∘=+130 kJ mol−1\Delta G^\circ = +130\,\text{kJ mol}^{-1} at 298 K298\,\text{K} • ΔG∘=−17 kJ mol−1\Delta G^\circ = -17\,\text{kJ mol}^{-1} at 1200 K1200\,\text{K} (1) Part 1: Without performing detailed calculations, compare the magnitude of the equilibrium constant, KK, at 298 K298\,\text{K} with its magnitude at 1200 K1200\,\text{K}. State which temperature yields the larger KK and provide a qualitative justification. (2) Part 2: Explain how the sign change in ΔG∘\Delta G^\circ with increasing temperature influences the position of equilibrium in an industrial kiln used to convert limestone (CaCO3\mathrm{CaCO_3}) to quicklime (CaO\mathrm{CaO}). (3) Part 3: Manufacturers often introduce a continuous flow of hot air through the kiln. Discuss how maintaining a low partial pressure of CO2(g)\mathrm{CO_2(g)} affects the thermodynamic favorability of the decomposition and the equilibrium constant. Link your explanation to Le Châtelier’s principle and the free-energy concepts presented above.

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