What is the effect of enzymes on activation energy and ΔG?

• A. Enzymes lower activation energy and do not change ΔG
• B. Enzymes increase activation energy and increase ΔG
• C. Enzymes do not affect activation energy but change ΔG
• D. Enzymes alter both activation energy and ΔG

Answer: (A)

Enzymes speed reactions by lowering the activation energy—the energy barrier that must be overcome to reach the transition state—without changing the overall free energy change (ΔG) of the reaction. In the active site, enzymes stabilize the transition state, properly orient substrates, and provide catalytic helpers, which together reduce the amount of energy needed to start the reaction. This accelerates both the forward and reverse directions equally, so the equilibrium position and ΔG remain the same.

That’s why the statement that enzymes lower activation energy and do not change ΔG is the best description. If a choice claimed enzymes increased activation energy or altered ΔG, it would contradict how catalysts function, since they modify the rate by lowering the barrier but do not alter the thermodynamic outcome of the reaction.