Question

Which factor is altered by a catalyst?

• A. Internal energy
• B. Activation energy
• C. Entropy
• D. Enthalpy

Hint:

Catalysts change the speed of a reaction, not the overall energetics of reactants and products.

Answer 1

The Correct Option is B

Concept: A catalyst changes the rate of a reaction by providing an alternative reaction pathway having lower activation energy.

Step 1: Understanding activation energy. Activation energy is the minimum energy required for reactant molecules to undergo effective collision and convert into products. Without catalyst: \[ E_a=\text{high} \] With catalyst: \[ E_a=\text{lower} \] Thus, more molecules acquire sufficient energy to react, increasing the reaction rate.

Step 2: Checking thermodynamic quantities. A catalyst affects only the kinetics of a reaction, not the thermodynamic properties. Therefore: \[ \Delta H,\ \Delta G,\ \Delta S \] remain unchanged. Similarly, internal energy also remains unchanged.

Step 3: Conclusion. Only activation energy is altered by a catalyst. Hence, option (2) is correct.