Question

According to adsorption theory of catalysis, the speed of the reaction increases because:

• A. Adsorption produces heat which increases the speed of the reaction.
• B. In the process of adsorption, the activation energy of the molecules becomes large.
• C. The concentration of the reactant molecules at the active centres of the catalyst becomes high due to adsorption.
• D. Adsorption lowers the activation energy of the reaction.

Answer 1

The correct option is C The concentration of the reactant molecules at the active centres of the catalyst becomes high due to adsorption.

In the video, we mentioned that when gases adsorb on the surface of a solid, the concentration of the gas increases on the surface. And this is quite easy to see, right? This is because the gas gets retained on the surface and on further adsorption the amount of gas adsorbed only increases and this means that the 'concentration' of gas keeps increasing.
The only thing is that we need to link this to what we learnt in chemical kinetics. We learnt that the rate of any reaction is directly proportional to the concentration of reactants. So this means that the rate of reaction would also increase with adsorption.
This is what the adsorption theory claims increases the rate of reaction due to adsorption.