The difference between exergonic and exothermic reactions is that energy is released to the surroundings in an exergonic reaction. When an exothermic reaction occurs, the energy released to the surroundings is heat energy.
In an exergonic reaction, the chemical bonds formed are stronger than those broken. When there is an exothermic reaction, the temperature of the surroundings increase. Two related terms are endergonic reaction and endothermic reaction. An endergonic reaction refers to energy being absorbed from the surroundings. When there is an endergonic reaction, the chemical bonds formed are weaker than those broken. An endothermic reaction describes when an endergonic reaction occurs and the energy being absorbed from the surroundings is heat energy. When there is an endothermic reaction, the temperature of the surroundings decrease.