Which description best fits an exothermic reaction in a calorimeter?

• A. The reaction absorbs heat from the surroundings, cooling the surroundings.
• B. Heat is transferred from the surroundings to the reaction.
• C. No heat is exchanged with the surroundings.
• D. The reaction releases heat to the surroundings, warming the surroundings.

Answer: (D)

Exothermic reactions release energy as heat. In a calorimeter, that heat flows from the reacting substances into the surroundings (the calorimeter itself and any surrounding water or air), which makes the surroundings warmer. This warming indicates heat transfer from the system to the surroundings, a hallmark of exothermic behavior. So the description that fits best is that the reaction releases heat to the surroundings, warming the surroundings. If heat were absorbed instead, the surroundings would cool, or if there were no heat exchange, there would be no temperature change.