Catalysts lower activation energy; temperature affects collision rates

Steps:

• Catalysts decrease activation energy, increasing reaction rate by enabling more successful collisions.
• Removing the catalyst raises activation energy back to original uncatalyzed level, slowing the reaction.
• Increasing temperature compensates by giving molecules more kinetic energy, raising collision frequency and proportion of successful collisions.
• To match original rate, new conditions have higher activation energy but more energetic collisions.

Why B is correct:

• Without catalyst, activation energy returns to its higher uncatalyzed value, per the Arrhenius equation where rate depends on e^(-Ea/RT).

Why the others are wrong:

• A: Activation energy increases without catalyst, not decreases.
• C: Higher temperature increases successful collisions to maintain rate.
• D: Successful collisions increase with temperature, but the key change is higher activation energy.

Final answer: B