In a reaction coordinate diagram, if the products are at a higher energy level than the reactants, which statements are true about ΔH and the reaction type?

In a reaction coordinate diagram, if the products are at a higher energy level than the reactants, which statements are true about ΔH and the reaction type?

• A. ΔH is positive; the reaction is endothermic
• B. ΔH is negative; the reaction is exothermic
• C. ΔH is zero; isothermal
• D. ΔH is positive; the reaction is exothermic

Answer: (A)

When you compare the energy of products to reactants on a reaction coordinate diagram, ΔH is the energy of products minus the energy of reactants. If the products are higher in energy, that difference is positive, meaning heat must be absorbed from the surroundings to reach the higher-energy products. That describes an endothermic process. So the statement that ΔH is positive and the reaction is endothermic fits the diagram perfectly. If ΔH were negative, the reaction would be exothermic; if ΔH were zero, there would be no net energy change between reactants and products; and labeling a positive ΔH as exothermic would be inconsistent. The option about isothermal isn’t the defining outcome here, since the energy change, not the temperature behavior alone, determines ΔH in this context.

When you compare the energy of products to reactants on a reaction coordinate diagram, ΔH is the energy of products minus the energy of reactants. If the products are higher in energy, that difference is positive, meaning heat must be absorbed from the surroundings to reach the higher-energy products. That describes an endothermic process. So the statement that ΔH is positive and the reaction is endothermic fits the diagram perfectly. If ΔH were negative, the reaction would be exothermic; if ΔH were zero, there would be no net energy change between reactants and products; and labeling a positive ΔH as exothermic would be inconsistent. The option about isothermal isn’t the defining outcome here, since the energy change, not the temperature behavior alone, determines ΔH in this context.