Which statement best distinguishes endothermic and exothermic reactions with respect to energy diagrams?

• A. Endothermic: energy of products lower than reactants; exothermic: energy of products higher than reactants.
• B. Endothermic: energy of products higher than reactants; exothermic: energy of products lower than reactants.
• C. Endothermic: no energy change; exothermic: energy change occurs.
• D. Endothermic: heat is released to surroundings; exothermic: heat is absorbed.

Answer: (B)

In energy diagrams, what matters is the sign of the enthalpy change: endothermic reactions absorb energy, so the products end up at higher energy than the reactants, while exothermic reactions release energy, leaving the products at lower energy than the reactants. The best description matches this by saying endothermic has higher-energy products than reactants and exothermic has lower-energy products than reactants. That aligns with energy diagrams showing the product energy level relative to the reactant energy level.

The other statements don’t fit because they either flip the energy relationship (endothermic having lower-energy products) or claim no energy change for one case, which isn’t true. Also, describing heat flow should align with which form of energy is stored in the system: endothermic systems absorb heat, exothermic systems release heat.