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

• A. The reactants start at a higher energy level, and the products are at a lower energy level.
• B. The activation energy is zero.
• C. The reactants start at a lower energy level, and the products are at a higher energy level.
• D. The reactants and products are at the same energy level.

Answer: (C)

Verified step by step guidance

1. Understand the definition of an endothermic reaction: it is a reaction that absorbs energy from the surroundings, meaning the products have higher energy than the reactants.
2. Recall that in an energy profile diagram, the vertical axis represents the potential energy of the system, while the horizontal axis represents the progress of the reaction.
3. Identify that for an endothermic reaction, the energy level of the products must be higher than that of the reactants, indicating energy absorption.
4. Note that the activation energy is the energy barrier that must be overcome for the reaction to proceed, and it is typically a positive value, not zero.
5. Conclude that the correct energy profile diagram for an endothermic reaction shows reactants at a lower energy level and products at a higher energy level, with a positive activation energy peak between them.