If a reaction is exothermic, what is true of its reverse reaction?

• A. The reverse reaction releases more energy than the forward reaction.
• B. The reverse reaction is also exothermic.
• C. The reverse reaction has no enthalpy change.
• D. The reverse reaction is endothermic.

Answer: (D)

Verified step by step guidance

1. Understand that an exothermic reaction releases energy to the surroundings, meaning its enthalpy change (\Delta H) is negative.
2. Recall that the reverse reaction involves the same reactants and products but in opposite directions, so the enthalpy change for the reverse reaction is the negative of the forward reaction's enthalpy change.
3. Since the forward reaction is exothermic (\Delta H < 0), the reverse reaction must absorb energy, making its enthalpy change positive (\Delta H > 0).
4. A reaction that absorbs energy from the surroundings is called endothermic, so the reverse reaction is endothermic.
5. Therefore, the correct statement is that the reverse reaction is endothermic, not exothermic or without enthalpy change.