Activation energy concept: what happens when a catalyst is present?

• A. It is increased
• B. It is lowered (correct)
• C. It remains unchanged
• D. It becomes negative

Answer: (B)

Catalysts provide an alternative reaction pathway with a lower activation energy, which is the energy barrier that must be overcome for reactants to reach the transition state and form products. By lowering this barrier, more molecules can reach the transition state at the same temperature, so the reaction rate increases. The overall energy difference between reactants and products remains the same, so catalysis speeds up the reaction without changing the final amounts or stability of the products. Catalysts are not consumed in the process, so they can facilitate many cycles.

Raising the barrier would slow the reaction, leaving the barrier unchanged wouldn’t explain a faster rate, and a negative activation energy isn’t a typical outcome of catalysis.