Chemical Reaction Engineering MCQ Questions & Answers | Chemical Engineering

Concept: In a solid-catalyzed reaction, reactant molecules must diffuse through the pores of the catalyst to reach the active sites where the reaction takes place.

Pore diffusion control: When pore diffusion is the controlling step, the overall reaction rate is limited by the movement of reactants within the pores rather than by the surface reaction itself.

Importance of porosity: Higher porosity provides more void space for reactant molecules to diffuse easily, reducing internal mass transfer resistance and improving access to active sites.

Reason: If the porosity is low, diffusion is hindered, and a large portion of the catalyst's active surface remains underutilized, decreasing the overall efficiency of the catalyst.

Conclusion: When pore diffusion controls the reaction, porosity is very important for effective catalyst performance.

According to the Arrhenius equation, the rate constant (k) increases with an increase in temperature.

The Arrhenius equation is given by: $$k = A \exp \left( -\frac{E_a}{RT} \right)$$.

Here, k is the rate constant, A is the pre-exponential factor, E_a is the activation energy, R is the gas constant, and T is the temperature in Kelvin.

As the temperature T increases, the exponential term becomes larger, leading to an increase in the rate constant.