Question

The lowering of activation energy by catalyst is due to :

• A. formation of adsorbed activated complex and to provide new pathway to reaction
• B. adsorption is always exothermic
• C. the adsorbed activated complex possesses lower energy level than simple activated complex
• D. all of the above

Answer 1

Answer: (D)

all of the above

A Catalyst is a substance which accelerates the rate of a chemical reaction without undergoing any change in its chemical composition or mass during the reaction. A catalyst accelerates the rate of a reaction by lowering the activation energy.

The activation energy of a reaction is the difference in energy between the initial state and the highest peak in the reaction energy curve (the highest-energy transition state).

A catalyst provides an alternative pathway for a reaction. Usually, this will be more complicated than the original, uncatalyzed reaction. From the diagram above, we can see that the hypothetical reaction proceeds in a single step without the catalyst, but takes four steps when catalyzed. However, the activation energy is lowered because each of the four steps has a lower-energy transition state than the original reaction.

$R\to \underset{\text{activate complex}}{Intermediate}\to Product$

$R+C\to \underset{adsorbed-activatedcomplex;\Delta H=-ve}{Intermediate}\to Product$