The standard Gibbs energy of reaction is the difference in standard molar Gibbs
energies of the products and reactants in their standard states at the temperature
specified for the reaction as written. As in the case of standard reaction enthalpies, it is
convenient to define the standard Gibbs energies of formation, ΔfG7, the standard
reaction Gibbs energy for the formation of a compound from its elements in their reference
states.7 Standard Gibbs energies of formation of the elements in their reference
states are zero, because their formation is a ‘null’ reaction. A selection of values for
compounds is given in Table 3.4. From the values there, it is a simple matter to obtain
the standard Gibbs energy of reaction by taking the appropriate combination