Question

Which of the following is affected by catalyst?
A.$\Delta H$
B.$\Delta S$
C.$\Delta G$
D.$E_a$

Answer 1

Any substance which changes the reaction rate without undergoing any chemical reaction and hence affecting the overall energetics of the reaction is called a Catalyst of that reaction. Catalysts typically speed up a reaction by changing its reaction mechanism or the path of reaction.

Complete answer:
-The heat of a reaction is the change in the enthalpy of a chemical reaction that occurs at a constant pressure. Enthalpy is a state function because it is derived from pressure, volume, and internal energy, all of which are state functions.
-The change in enthalpy of the chemical does not depend on the path taken for that chemical reaction; hence it is independent of any effect by catalysts.
-$\Delta S$ is the entropy of a reaction, which is a measurement of randomness of a reaction from reactants to products. The entropy change in a chemical reaction is given by the sum of the entropies of the products minus the sum of the entropies of the reactants. Hence it is also unaffected by catalysts because it is independent of the path of the reaction.
-$\Delta G$ is the change in the free energy(or Gibbs free energy) of a system. $\Delta G$can be calculated for any system that undergoes a change, like chemical reactions. system. The formula for calculating ∆G is as follows: $G=\Delta H-T\Delta S$, where $\Delta H$ is the total energy change in the system or the enthalpy of the system and T is the absolute temperature of the system in Kelvin.
-As we can see that Gibbs free energy is only determined by the enthalpy and entropy of reactants and products and since they are unaffected by catalysts, Gibbs free energy or change in Gibbs free energy is also not affected by catalysts.
-A catalyst is a substance that increases the reaction rate without getting consumed in the process. -Catalysts speed up the reactions by reducing the activation energy(Ea) or changing the reaction mechanism(path of a reaction). Activation energy is thus affected by the use of catalysts, therefore the answer is option D, Ea.
Thus, the answer to our question is option D.

Note:
In chemical kinetics the whole purpose of using catalysts is to reduce the activation energy of the reactions. The catalysts do this by altering the path of the reaction from an uncatalyzed path.