Chemical Equilibria

The standard free energy of formation, ΔGo and the equilibrium constant, K are related by the expression, ΔGo = − RT ln K. Hence the measurement of equilibrium constant under various conditions would give the thermodynamic data such as free energy, enthalpy and entropy and partial quantities. However, slow attainment of chemical equilibrium in many systems, especially where all the phases are present in the solid state limits the applicability of this technique. The systems involving gases and vapors can be most conveniently studied. The studies on reaction equilibria between gases and condensed phases require the exposure of the condensed phase to gas mixture with accurately controlled chemical potentials. The required chemical potentials can be established by using appropriate gaseous mixtures. A brief account on gaseous mixtures used for controlling the chemical potentials of some of the common elements together with experimental methods for preparation of gas mixtures have been included in this chapter. Different types of equilibria viz., solid-liquid-gas, solid-gas, molten metal-gas, metal-slag-gas, solid-liquid, and liquid-liquid have been discussed.