Question

In the exothermic reaction, the enthalpy of reaction is always

• A. zero
• B. positive
• C. negative
• D. None of these

Answer 1

Answer: (C)

negative

Exothermic and endothermic reactions cause energy level differences and therefore differences in enthalpy $\left(\Delta H\right)$, the sum of all potential and kinetic energies. $\Delta H$ is determined by the system, not the surrounding environment in a reaction. A system that releases heat to the surroundings, an exothermic reaction, has a negative $\Delta H$ by convention, because the enthalpy of the products is lower than the enthalpy of the reactants of the system.