Catalysts increase ______ by ______.

• A. Equilibrium by changing enthalpy
• B. Energy by increasing temperature
• C. Reaction rates by increasing activation energy
• D. Reaction rates by lowering activation energy of reaction (correct)

Answer: (D)

Catalysts work by providing an alternative reaction path that has a lower activation energy. This lowers the energy barrier that reactants must overcome to reach the transition state, so more molecules can react per unit time and the reaction speeds up. Importantly, catalysts don’t change the overall energy change of the reaction or the temperature; they don’t alter enthalpy or directly raise temperature, and they don’t shift the equilibrium position—they speed up both forward and reverse reactions equally, leaving the equilibrium constant unchanged. So the correct idea is that catalysts increase reaction rates by lowering activation energy.