Question: The role of a catalyst is to change :
Step 1 (Governing Principle): [0.5 Mark]
According to the Collision Theory and the Arrhenius equation, the rate constant $k$ of a reaction is given by:
$$k = A e^{-E_a / RT}$$Where $E_a$ represents the activation energy. A catalyst provides an alternative reaction pathway with a lower activation energy ($E_a' < E_a$), thereby increasing the rate of the reaction without altering the thermodynamic properties of the system.
Step 2 (Analysis of Thermodynamic Parameters): [0.25 Mark]
- Equilibrium Constant ($K_{eq}$): Depends only on temperature ($T$). A catalyst speeds up both forward and backward reactions equally, leaving $K_{eq}$ unchanged.
- Enthalpy ($\Delta H$) and Gibbs Energy ($\Delta G$): These are state functions determined by the initial and final states of the reactants and products. A catalyst does not change the energy levels of the reactants or products.
Step 3 (Final Concluded Answer): [0.25 Mark]
Since the catalyst only lowers the energy barrier for the reaction to proceed, the correct option is (D) activation energy of reaction.
💡 EL10 Concept Insight: Think of a catalyst like a tunnel through a mountain; it doesn't change the height of the mountain (enthalpy) or where you start and end (Gibbs energy), it just gives you a much easier, lower path to get to the other side faster!