In an exothermic reaction, how does the energy of products compare to the energy of reactants?

• A. Energy of products is higher than that of reactants.
• B. Energy of products is the same as that of reactants.
• C. In an exothermic reaction, the energy of products is lower than that of reactants.
• D. Cannot be determined from given information.

Answer: (C)

In an exothermic reaction, energy is released to the surroundings, so the products end up with less stored energy than the reactants. The bonds formed in the products store less energy than the bonds broken in the reactants, and the excess energy is emitted as heat, which is why the surroundings often get warmer. That’s why the correct statement is that the energy of the products is lower than the energy of the reactants.

If the products had higher energy, that would mean energy was absorbed from the surroundings, which describes an endothermic process. If the energies were the same, there would be no energy change at all, contradicting the exothermic nature. If nothing could be determined, we wouldn't have a definite statement about the energy change in an exothermic reaction.