D20.4 Calculating ΔG°
A convenient and common approach to calculate ΔrG° for reactions is by using standard state thermodynamic data. One method involves first determining the ΔrH° and ΔrS°, then using the equation:
Exercise: Standard Gibbs Free Energy Change from Enthalpy and Entropy Changes
It is also possible to use the standard Gibbs free energy of formation (ΔfG°) of the reactants and products involved in the reaction to calculate ΔrG°. ΔfG° is the Gibbs free energy change that accompanies the formation of one mole of a substance from its elements in their standard states. It is by definition zero for the most stable form of an elemental substance under standard state conditions. (Note that tabulated ΔfG° values are often specified at 298 K, therefore using such values to calculate ΔrG° is only valid at 298 K.)
For a generic reaction:
ΔrG° from ΔfG° would be:
Exercise: Calculating Standard Gibbs Free Energy Change
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