Question

Does an enzyme change the equalibrium concentrations of reactants and products? please explain in detail.

Answer 1

An enzyme is a bio-catalyst. So, the enzyme is only used to speed up the reaction process. Suppose, a reaction from A to B needs a high activation energy barrier. The utility of a catalyst or enzyme is that it creates an alternative route for the reaction via some intermediate, in which the activation energy barrier is quite low. Like the diagram given-

RED = without catalyst, GREEN = with catalyst

Clearly, catalyst creates a low energy path.

Now, if we talk about a reversible reaction A to B then it is inherent property of the reaction that it will have a forward (A to B) as well as a backward reaction (B to A) and they will go simulteneously. If we add catalyst to the reaction medium, then that will create a low energy path for the forward reaction, where the reactant A will go to product B. But, the product can also use the same pathway to come back at reactant according to the microscopic reversibility. So catalyst actually increases the rate of forward reaction as well as the backward reaction.

Now, we know the expression of the equilibrium constant, i.e, the ratio of rate constants of forward and backward reaction. Also, if we consider the reaction, , then at equilibrium the rate of forward reaction is equal to the rate of backward reaction. Thus, from chemical kinetics, , [ ] denotes concentration.

therefore we can write, . Since enzyme increases both k_f and k_b in same extent thus, there is no change in the ratio, so K_eq doesnot change and also the ratio of concentrations of B and A doesn't change. So, the equilibrium concentrations [A] and [B] doesn't change. Now, you may argue they are both increasing or decreasing in the same extent. But that is not possible since, the total concentration in the reaction vessel is fixed, that can't be altered.