Which of the following best describes what happens in an exothermic reaction?

• A. Energy is released to the surroundings, usually in the form of heat.
• B. The products have higher enthalpy than the reactants.
• C. No energy change occurs between the system and the surroundings.
• D. Energy is absorbed from the surroundings, causing the temperature to decrease.

Answer: (A)

Verified step by step guidance

1. Understand the definition of an exothermic reaction: it is a chemical reaction that releases energy to the surroundings, often as heat.
2. Recall that enthalpy (H) is a measure of the total heat content of a system. In an exothermic reaction, the enthalpy of the products is lower than that of the reactants because energy is released.
3. Recognize that if energy is released, the surroundings gain energy, which usually causes an increase in temperature.
4. Contrast this with endothermic reactions, where energy is absorbed from the surroundings, causing a temperature decrease.
5. Therefore, the best description of an exothermic reaction is that energy is released to the surroundings, usually in the form of heat.