In this approach, all three species taking part in the reaction, including the electron, must be placed in thermodynamically well-defined states.
To express this in volts one divides the Gibbs free energy by the negative of Faraday's constant.
[4] An alternative definition of the absolute half-cell entropy has recently been published by Fang et al.[5] who define it as the entropy of the following reaction (using the hydrogen electrode as an example): This approach differs from the approach described by Rockwood in the treatment of the electron, i.e. whether it is placed in the gas phase or the metal.
This near-agreement in the numerical value depends on the choice of ambient temperature and standard states, and is the result of the near-cancellation of certain terms in the expressions.
However, there is no fundamental significance to this near agreement because it depends on arbitrary choices, such as temperature and definitions of standard states.