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

• A. The energy of the products is lower than the energy of the reactants; heat is released.
• B. The energy of the products is higher than the energy of the reactants; heat is absorbed.
• C. The energy of the products is the same as the energy of the reactants.
• D. Energy change is independent of temperature or heat transfer.

Answer: (A)

Exothermic reactions release energy to the surroundings. That means the chemical energy of the reactants is higher than the energy of the products, so the products end up with less energy and heat is given off. The overall enthalpy change is negative, and you’d notice the surroundings warming as the reaction proceeds. If the products had more energy, the reaction would be endothermic and absorb heat. If the energies were the same, there would be no energy change. The statement about energy change being independent of temperature or heat transfer doesn’t fit exothermic behavior, which is all about releasing heat.