Q. Explain Le Chtelier's Principle

Ans.

Consider the equilibrium reaction of:

A + B -> C + D

The forward reaction occurs when A and B combine to form C and D:

A + B -> C + D

The reverse reaction occurs when C and D combine to form A and B:

C + D -> A + B

At equilibrium, A, B, C, and D are present. The concentrations of these substances remain constant, providing that the conditions are unchanged.

If the forward reaction is favored, a new equilibrium will be established for which the concentrations of the products C and D will increase while the concentrations of the reactants A and B will decrease. In this case, the equilibrium is said to move to the right.

On the other hand, if the reverse reaction is favored, a new equilibrium will be established for which the concentrations of the products A and B will increase while the concentrations of the reactants C and D will decrease. In this case, the equilibrium is said to move to the left.

We can predict how an equilibrium reacts to change by a relatively simple principle. The principle was discovered by the French chemist Le Chtelier in 1888. His discovery, known as the Le Chtelier's Principle, may be stated as follows:

When a system in equilibrium is subject to a change in conditions, the equilibrium will tend to move in such a way as to minimize the change.

Applying Le Chtelier's Principle to the above equilibrium reaction, we can say the following:

If the equilibrium conditions favor the formation of C and D, this change will be minimized by an increase in the formation of A and B.
If the equilibrium conditions favor the formation of A and B, this change will be minimized by an increase in the formation of C and D.