Chemical Thermodynamics

Chapter 9

Phase Equilibria

9.a.  Chemical Potential and Phase Equilibria

Consider a single component being present in two phases in equilibrium at constant temperature T and pressure P e.g., liquid water coexisting with water vapour at 298 K and 1 bar pressure. As long as the two phases coexist, material transport from one phase to the other does not affect the state of equilibrium at constant T and P. In a closed system of variable volume, when liquid and vapour coexist in equilibrium, at constant temperature and pressure, if the volume changes, the amount of the liquid phase and vapour phase will change to maintain equilibrium. The transfer of matter from gas phase to liquid phase or vice versa does not affect the state of equilibrium. Hence ...