The parameters that are different for a reaction carried out in the presence of a catalyst compared to the same reaction carried out in the absence of a catalyst are the activation energy (ΔH‡), overall enthalpy change (Ea), and rate constant (k).
When a reaction is carried out in the presence of a catalyst, the parameters that are different compared to the same reaction carried out in the absence of a catalyst are:
- ΔH‡: The activation energy of the reaction, which is the energy required for the reaction to proceed, is lower in the presence of a catalyst.
- Ea: The overall enthalpy change of the reaction remains the same whether a catalyst is present or not.
- k: The rate constant of the reaction is affected by the presence of a catalyst, leading to an increase in the rate of the reaction.
A catalyst affects a chemical reaction by lowering its activation energy, activation enthalpy, activation Gibbs free energy, activation entropy, and increasing the reaction rate constant, but does not alter the Gibbs free energy change, enthalpy change, standard entropy change, or the equilibrium constant of the reaction.
The presence of a catalyst affects the rate at which the reaction reaches equilibrium by offering a path with lower activation energy, although it does not alter the position of the equilibrium itself. This implies that once equilibrium is established, the concentrations of reactants and products remain the same, regardless of whether a catalyst was used or not. Consequently, the presence of a catalyst does not affect the equilibrium state of the reaction, reflected in the constant values of ΔG°, ΔH°, ΔS°, and Keq.