Calculating DGorxn
EXAMPLE 3: Combustion of carbon
C(graphite) + O2(g) ? CO2(g)
DGorxn = DGfo(CO2) - [DGfo(graph) + DGfo(O2)]
DGorxn = -394.4 kJ - [ 0 + 0]
Note that free energy of formation of an element in its standard state is 0.
Reaction is product-favored as expected.
DGorxn = S DGfo (products) - S DGfo (reactants)