In an endothermic reaction, Ea forward is ______ Ea reverse.

In an endothermic reaction, Ea forward is ______ Ea reverse.

• A. larger
• B. equal
• C. smaller
• D. none

Answer: (C)

In a reversible reaction, activation energy is the energy barrier to reach the transition state from the starting side. For an endothermic process, the products end up at a higher energy than the reactants, while the transition state sits at a higher energy still. The forward activation energy is the difference between the transition state and the reactants, whereas the reverse activation energy is the difference between the transition state and the products. Since the products are already at a higher energy than the reactants, the gap from the products up to the transition state is smaller than the gap from the reactants up to the transition state. In other words, Ea_forward is greater than Ea_reverse. A quick way to see this is Ea_forward = T − R and Ea_reverse = T − P; with P > R, Ea_forward > Ea_reverse. The energy profile shows the forward barrier is the larger hurdle, so the correct completion is that Ea forward is larger.

In a reversible reaction, activation energy is the energy barrier to reach the transition state from the starting side. For an endothermic process, the products end up at a higher energy than the reactants, while the transition state sits at a higher energy still. The forward activation energy is the difference between the transition state and the reactants, whereas the reverse activation energy is the difference between the transition state and the products.

Since the products are already at a higher energy than the reactants, the gap from the products up to the transition state is smaller than the gap from the reactants up to the transition state. In other words, Ea_forward is greater than Ea_reverse. A quick way to see this is Ea_forward = T − R and Ea_reverse = T − P; with P > R, Ea_forward > Ea_reverse. The energy profile shows the forward barrier is the larger hurdle, so the correct completion is that Ea forward is larger.