The determination of the equilibrium constant in systems involving multiple phases requires specific considerations. In heterogeneous equilibria, reactants and products exist in different phases, such as solids, liquids, and gases. The activity of a pure solid or liquid is considered unity and does not appear in the equilibrium constant expression. For instance, in the decomposition of calcium carbonate (CaCO3(s) CaO(s) + CO2(g)), only the partial pressure of carbon dioxide (CO2) dictates the equilibrium position. The concentrations of the solid calcium carbonate and calcium oxide are not included in the equilibrium constant (Kp = PCO2) calculation.
Accurately evaluating the equilibrium constant for these multiphase systems is crucial in various chemical engineering processes, environmental studies, and materials science. It allows for the prediction of reaction yields, optimization of process conditions, and understanding of geochemical reactions in natural environments. Historically, understanding these relationships has been vital in the development of industrial processes, such as the Haber-Bosch process, which involves a gas-solid heterogeneous catalyst. It also has applications in the study of mineral dissolution and precipitation, where phase boundaries play a significant role in reaction kinetics.
