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. And one example of a spontaneous reaction in nature is combustion. So combustion reactions are examples of exergonic reactions where the Delta G value is negative. Now, what about the opposite?