Jesse E. answered • 04/29/20
Masters in Chemistry and Bachelors in Biology
Mathematically, this can be done by looking at the standard bond energies. Once this is calculated, you can look at the total energy at each side of the reaction. To avoid confusion I am going to quote a textbook:
"In some reactions, the energy that must be absorbed to break the bonds in the reactants, is less than the energy that is released when the new bonds of the products are formed. This means that in the overall reaction, energy is released as either heat or light. This type of reaction is called an exothermic reaction...In other reactions, the energy that must be absorbed to break the bonds in the reactants, is more than the energy that is released when the new bonds in the products are formed. This means that in the overall reaction, energy must be absorbed from the surroundings. This type of reaction is known as an endothermic reaction."
