Which component of a chemical reaction is affected when a catalyst is added?

• A. The overall stoichiometry of the reaction
• B. The enthalpy change (ΔH) of the reaction
• C. The activation energy of the reaction
• D. The equilibrium constant of the reaction

Answer: (C)

Verified step by step guidance

1. Understand that a catalyst is a substance that increases the rate of a chemical reaction without being consumed in the process.
2. Recall that the overall stoichiometry of a reaction describes the relative amounts of reactants and products and is not changed by the presence of a catalyst.
3. Recognize that the enthalpy change (\$\Delta H\$) of a reaction is a state function dependent only on the initial and final states, so it remains unchanged by a catalyst.
4. Know that the activation energy is the energy barrier that must be overcome for reactants to convert into products, and a catalyst lowers this activation energy, making the reaction proceed faster.
5. Understand that the equilibrium constant depends on the free energy difference between reactants and products and is not affected by a catalyst, since catalysts speed up both forward and reverse reactions equally.