Question

The addition of a catalyst during a chemical reaction alters which of the following quantities ?

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

Answer 1

The Correct Option is C

To determine which quantity is altered by the addition of a catalyst during a chemical reaction, we should first understand the role of a catalyst in chemical processes.

Role of a Catalyst: A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. It does this by providing an alternative reaction pathway with a lower activation energy than the uncatalyzed pathway.

• Internal Energy: The addition of a catalyst does not change the internal energy of the reactants or products in a chemical reaction. It remains the same because internal energy is a state function and independent of the path taken.
• Enthalpy: The catalyst does not affect the enthalpy change of the reaction. Enthalpy change depends on the energy difference between products and reactants, which is not altered by the presence of a catalyst.
• Activation Energy: A catalyst reduces the activation energy required for a reaction. By lowering the activation energy, a larger number of molecules have energies exceeding this threshold, thereby increasing the reaction rate. Hence, this is the correct answer.
• Entropy: Similar to internal energy, entropy is a state function and is not directly changed by the presence of a catalyst.

Based on the above explanations, the correct answer is that a catalyst alters the activation energy of a reaction.

Conclusion: The correct option is Activation energy, as the catalyst provides an alternate pathway that requires lower energy for the reaction to proceed.