Читать книгу Geochemistry - William M. White - Страница 96

We define μ as the chemical potential, which is simply the partial molar Gibbs free energy:

(3.13)

The chemical potential thus tells us how the Gibbs free energy will vary with the number of moles, n_i, of component i holding temperature, pressure, and the number of moles of all other components constant. We said that the Gibbs free energy of a system is a measure of the capacity of the system to do chemical work. Thus, the chemical potential of component i is the amount by which this capacity to do chemical work is changed for an infinitesimal addition of component i at constant temperature and pressure. In a NiCd battery (common rechargeable batteries), for example, the chemical potential of Ni in the battery (our system) is a measure of the capacity of the battery to provide electrical energy per mole of additional Ni for an infinitesimal addition.

The total Gibbs free energy of a system will depend on composition as well as on temperature and pressure. The equations we introduced for Gibbs free energy in Chapter 2 fully describe the Gibbs free energy only for single component systems or systems containing only pure phases. The Gibbs free energy change of a phase of variable composition is fully expressed as:

(3.14)