Question

Which of the following factors are equal in a reversible chemical reaction at equilibrium?
A.The number of moles of the reactants and products
B.The potential energies of the reactants and products
C.The activation energies of the forward and reverse reactions
D.The rates of reaction for the forward and reverse reactions
E.The concentrations of the reactants and products

Answer 1

Hint: The state of the system in which the measurable properties of the system such as concentration, pressure, density, colour, etc. do not undergo any further noticeable change is referred as a state of equilibrium.
For a given overall composition of the system, the same equilibrium is reached whether equilibrium is approached from the reactants side or from the products side.

Complete step by step answer:
-After attainment of chemical equilibrium, the observable properties of the system like pressure and concentration become constant. Thus, the reactants and products in a state of equilibrium are present in concentrations which have no tendency to change thereafter.
-In the beginning of the reversible chemical reaction, the concentration of the reactants are large and those of the products are zero and so, only the forward reaction takes place but with the passage of time, the concentration of the reactants goes on decreasing and so is the rate of forward reaction.
-Whereas, the concentration of the products goes on increasing and so is the rate of the backward reaction. Finally, a state is reached at which the rate of the forward reaction becomes exactly equal to the rate of the backward or reverse reaction and the concentration of the reactants and products become constant and after that, does not change with time. -This particular state is the state of chemical equilibrium.
Thus, at equilibrium, the rates of the two opposing reactions become equal. So. Statement D is true.
-The concentrations of the reactants in equilibrium are not equal to that of the products. As a result, the number of moles (which is directly proportional to the concentration) of reactants are also not equal to that of the products. Therefore, the statements E and A are wrong.
-In an equilibrium reaction, the activation energy for the forward reaction is higher than that for the reverse reaction. Hence, they cannot be equal and so option C is also wrong.

Hence option D is correct.

Note:
-A catalyst is a compound that speeds up the rate of a chemical reaction without itself being consumed.
-In a reversible chemical equation, the addition of a catalyst leads to an equal speed up of both the forward and the reverse reactions, thereby allowing the system to reach the equilibrium faster than in the absence of a catalyst.
-However, it does not have any effect on the state of the equilibrium. It only helps to attain it faster.