Cantera 2.6.0

Electric Properties of Phases
Models of Phases of Matter

Computation of the electric properties of phases.

Collaboration diagram for Electric Properties of Phases:

Computation of the electric properties of phases.

### Treatment of the phase potential and the electrochemical potential of a species

The electrochemical potential of species \(k\) in a phase \(p\), \( \zeta_k \), is related to the chemical potential via the following equation,

      \f[
           \zeta_{k}(T,P) = \mu_{k}(T,P) + z_k \phi_p
      \f]

where \( \nu_k \) is the charge of species \(k\), and \( \phi_p \) is the electric potential of phase \(p\).

The potential \( \phi_p \) is tracked and internally stored within the base ThermoPhase object. It constitutes a specification of the internal state of the phase; it's the third state variable, the first two being temperature and density (or, pressure, for incompressible equations of state). It may be set with the function, ThermoPhase::setElectricPotential(), and may be queried with the function ThermoPhase::electricPotential().

Note, the overall electrochemical potential of a phase may not be changed by the potential because many phases enforce charge neutrality:

      \f[
           0 = \sum_k z_k X_k
      \f]

Whether charge neutrality is necessary for a phase is also specified within the ThermoPhase object, by the function call ThermoPhase::chargeNeutralityNecessary(). Note, that it is not necessary for the IdealGas phase, currently. However, it is necessary for liquid phases such as DebyeHuckel and HMWSoln for the proper specification of the chemical potentials.

This equation, when applied to the \( \zeta_k \) equation described above, results in a zero net change in the effective Gibbs free energy of the phase. However, specific charged species in the phase may increase or decrease their electrochemical potentials, which will have an effect on interfacial reactions involving charged species, when there is a potential drop between phases. This effect is used within the InterfaceKinetics and EdgeKinetics kinetics objects classes.

### Electrothermochemical Properties of Phases of Matter

The following classes are used to compute the electrical and electrothermochemical properties of phases of matter. The main property currently is the dielectric constant, which is an important parameter for electrolyte solutions. The class WaterProps calculate the dielectric constant of water as a function of temperature and pressure.

WaterProps also calculate the constant A_debye used in the Debye Huckel and Pitzer activity coefficient calculations.