Which of the following best defines an exothermic reaction?

• A. A reaction that absorbs heat from its surroundings
• B. A reaction that occurs only at high temperatures
• C. A reaction in which the products have higher enthalpy than the reactants
• D. A reaction that releases heat to its surroundings

Answer: (D)

Verified step by step guidance

1. Understand the concept of enthalpy (\( \Delta H \)) in chemical reactions, which represents the heat content of a system.
2. Recall that an exothermic reaction is one where heat is released to the surroundings, meaning the system loses heat.
3. Recognize that when heat is released, the enthalpy of the products is lower than that of the reactants, so \( \Delta H < 0 \).
4. Contrast this with an endothermic reaction, where heat is absorbed from the surroundings and \( \Delta H > 0 \).
5. Therefore, the best definition of an exothermic reaction is one that releases heat to its surroundings.