In a reaction coordinate diagram, ∆H is defined as the energy difference between which states?

In a reaction coordinate diagram, ∆H is defined as the energy difference between which states?

• A. Activation energy and transition state
• B. Reactants and products
• C. Transition state and products
• D. Reactants and transition state

Answer: (B)

Delta H is the overall energy change of the reaction, equal to the difference in energy between products and reactants on a reaction coordinate diagram. On the diagram, reactants sit at one energy level and products at another; delta H = E_products − E_reactants. If delta H is negative, the reaction is exothermic (releases heat); if positive, it’s endothermic (absorbs heat). This is different from the activation energy, which is the energy needed to climb from the reactants up to the transition state (the energy barrier). The energy difference from the transition state to the products is the reverse activation energy. So, the energy difference between reactants and products is the quantity that represents delta H.

Delta H is the overall energy change of the reaction, equal to the difference in energy between products and reactants on a reaction coordinate diagram. On the diagram, reactants sit at one energy level and products at another; delta H = E_products − E_reactants. If delta H is negative, the reaction is exothermic (releases heat); if positive, it’s endothermic (absorbs heat). This is different from the activation energy, which is the energy needed to climb from the reactants up to the transition state (the energy barrier). The energy difference from the transition state to the products is the reverse activation energy. So, the energy difference between reactants and products is the quantity that represents delta H.