Question

Select the right option about a catalyst.

• A. Changes $\Delta G$ for a reaction.
• B. Acts by increasing the rate of the forward reaction more than the reverse reaction.
• C. Raises the equilibrium constant of a system.
• D. May have a molecular weight as low as 1 or higher than 200,000

Answer 1

The correct option is D May have a molecular weight as low as 1 or higher than 200,000

Catalyst may have a molecular weight as low as 1 or higher than 200,000.
Catalysts work by providing an (alternative) mechanism involving a different transition state and lower activation energy. Consequently, more molecular collisions have the energy needed to reach the transition state. Hence, catalysts can enable reactions that would otherwise be blocked or slowed by a kinetic barrier. The catalyst may increase reaction rate or selectivity, or enable the reaction at lower temperatures. This effect can be illustrated with an energy profile diagram.

Generic potential energy diagram showing the effect of a catalyst in a hypothetical exothermic chemical reaction X + Y to give Z.

The presence of the catalyst opens a different reaction pathway (shown in red) with a lower activation energy. The final result and the overall thermodynamics are the same.

Here, the correct option is only D.