A reaction diagram shows a forward activation energy Ea and an enthalpy change delta H. What is the activation energy of the reverse reaction?
AThe difference of Ea minus delta H
BThe same value of Ea as the forward
CThe value of delta H taken alone
DThe sum of Ea and delta H together
Answer & Solution
Correct answer: D. The sum of Ea and delta H together
1. On the energy diagram the transition state peak sits Ea above the reactants.
2. The products sit delta H below the reactants for the drawn case, so the peak stands even further above the products.
3. Climbing from products back to the same peak therefore takes Ea plus delta H.
4. Using Ea alone ignores that the reverse climb starts from a different energy level.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 12 "Kinetics", section 12.5 Collision Theory_
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