Question

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

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

Answer 1

The Correct Option is D

The adsorption theory of catalysis explains how catalysts increase the rate of chemical reactions. According to this theory, catalysts work by adsorbing reactant molecules onto their surface. This process influences the reaction in the following ways:

• Adsorption Lowers Activation Energy: When the reactant molecules are adsorbed onto the surface of the catalyst, the bonds within these molecules are weakened. This effectively lowers the activation energy required for the reaction to proceed. With lower activation energy, more molecules can participate in the reaction, thus increasing the reaction rate.
  E_a({'on\ catalyst'}) < E_a({'without\ catalyst'})
  This is the accurate explanation as it aligns with the correct answer: Adsorption lowers the activation energy of the reaction.
• Concentration at Active Centers: While adsorption does result in a higher concentration of reactant molecules at the catalyst surface, it is not the primary reason for the acceleration of reaction rate. The key factor remains the decrease in activation energy.
• Heat Production: The process of adsorption can indeed release heat (exothermic process), but this is not the main reason the reaction speed increases. The crucial factor is still the reduction in the activation energy.
• Does Not Increase Activation Energy: The notion that activation energy increases during adsorption is incorrect. Instead, it is reduced, as mentioned earlier, allowing the reaction to occur more readily.

In conclusion, the adsorption theory of catalysis demonstrates that the primary reason for the increased speed of the reaction is the reduction in activation energy, which allows more reactant molecules to reach the energy barrier necessary for the reaction to proceed.