Which statement best describes endothermic and exothermic processes and how energy transfer is depicted on an energy diagram?

• A. An exothermic process absorbs energy, so the products end up at higher energy than the reactants; the activation energy is not shown.
• B. An endothermic process releases energy, and activation energy is always zero.
• C. On a diagram, endothermic shows products at higher energy than reactants; activation energy is shown as a barrier; catalysts lower the barrier.
• D. A catalyst always raises the activation energy to slow the reaction.

Answer: (C)

Energy diagrams show how energy changes as a reaction proceeds, highlighting whether energy is absorbed or released and where the reaction must climb to reach the transition state. Endothermic processes require energy input, so the products end up at higher energy than the reactants. On the diagram, this shows as a rise from reactants to products, with the vertical difference representing the absorbed energy. The reaction must go over an activation barrier—the peak between reactants and products—which is the activation energy. A catalyst provides an alternative pathway with a lower barrier, so the peak is lower when a catalyst is present. This combination—products at higher energy, the activation-energy barrier depicted, and the barrier being lowered by a catalyst—is why this statement is the best choice. The other options contradict basic ideas (exothermic releases energy with products at lower energy; activation energy isn’t always zero; catalysts don’t raise the barrier).