Which of the following energy profile diagrams best represents an exothermic reaction?

• A. The reactants start at a lower energy level than the products, with the energy increasing as the reaction proceeds.
• B. The reactants and products are at the same energy level, with no net change in energy.
• C. The energy of the system remains constant throughout the reaction.
• D. The reactants start at a higher energy level than the products, with the energy decreasing as the reaction proceeds.

Answer: (D)

Verified step by step guidance

1. Understand that an exothermic reaction releases energy to the surroundings, so the products have less energy than the reactants.
2. Visualize the energy profile diagram: the vertical axis represents energy, and the horizontal axis represents the progress of the reaction.
3. In an exothermic reaction, the energy level of the reactants is higher than that of the products, indicating energy is lost during the reaction.
4. Look for a diagram where the curve starts at a higher energy level (reactants) and ends at a lower energy level (products), showing a downward trend.
5. Confirm that the difference in energy between reactants and products corresponds to the energy released, which is characteristic of exothermic reactions.