Now, to calculate mathematically the gives free energy of this reaction, all we have to do is take the free energy of the products and subtract the free energy of the reactants. And that gives us the gives free energy given by Delta G. So this quantity here is how much energy is going to be released in this reaction. And it's basically how much energy we can use in some process. Now, for this particular case, this reaction describes an exergonic reaction. And exergonic reactions always have a negative Delta G. That means energy is released in this reaction and the reaction is said to be spontaneous. So a chemical reaction is said to be exergonic and spontaneous if the Delta G is negative.