Which of the following energy profile diagrams best illustrates the effect of a catalyst on the rate of a chemical reaction?

• A. A diagram where the activation energy is higher for the catalyzed reaction than for the uncatalyzed reaction.
• B. A diagram where the energies of the reactants and products are changed by the presence of a catalyst.
• C. A diagram where the catalyst increases the overall energy change (ΔH) of the reaction.
• D. A diagram where the activation energy is lower for the catalyzed reaction compared to the uncatalyzed reaction, but the reactants and products have the same energies.

Answer: (D)

Verified step by step guidance

1. Understand that a catalyst works by providing an alternative reaction pathway with a lower activation energy, which increases the reaction rate without being consumed in the process.
2. Recall that the activation energy (E_a) is the energy barrier that must be overcome for reactants to be converted into products; a catalyst lowers this barrier.
3. Note that a catalyst does not change the energies of the reactants or products, so the overall energy change of the reaction (ΔH) remains the same.
4. Recognize that in an energy profile diagram, the presence of a catalyst is shown by a lower peak (activation energy) for the catalyzed reaction compared to the uncatalyzed reaction, while the starting and ending energy levels stay constant.
5. Therefore, the correct energy profile diagram will show the catalyzed reaction with a lower activation energy peak but identical reactant and product energy levels, illustrating the catalyst's effect on the reaction rate without altering ΔH.