Page 149 - Instant notes

Electrochemical thermodynamics 135

where n is the number of moles of electrons transferred in the cell reaction (equal to the
number of electrons in each half-cell reaction when the cell reaction is obtained) and F is
Faraday’s constant, the charge on a mole of electrons.
For this and all other thermodynamic equations in this section, under the particular
condition of standard states this general equation applies. This

and since (see Topic C1),

measurement of allows calculation of K, the equilibrium constant for the formal cell
reaction (see Topic E5).
The change in entropy, ∆S cell, due to the cell reaction at any temperature is given by:

and the change in enthalpy, ∆H cell, is:

The change in volume, ∆V cell, for the cell reaction is:

These can be calculated from measurements of E cell and its variation with temperature, T,
at constant pressure, p, or with pressure at constant temperature around the conditions of
interest.
These relationships also apply to the standard half-cell reactions, as and
are zero for the SHE half-cell reaction , by definition, so that:

and