Problem: If I had a mole of methane, and I react that with two moles of oxygen, I'll produce a mole of carbon dioxide and two moles of water. What we want to answer is whether this reaction is spontaneous. 

To determine the spontaneity of this reaction we would have to determine the Gibbs free energy (ΔG) of reaction using the equation below. 

$\boxed{∆G° = \sum _{}n∆G{°}_{f products} - \sum _{}m∆G{°}_{f reactants}}$

where: n and m are the coefficients of the balanced reaction. 

Recall that if:

• ΔG < 0 or ΔG = (–); the reaction is spontaneous

• ΔG = 0; the reaction is at equilibrium

• ΔG > 0 or ΔG = (+); the reaction is non-spontaneous