When the reaction parameters like concentration, pressure, or temperature are changed for a reversible reaction at equilibrium, the equilibrium shifts toward the reactants or the products in such a way that the change (or stress) is minimized, and the equilibrium is restored. this is known as le châtelier’s principle.
for example, consider the general reversible reaction a⇌b.

the equilibrium expression for this reaction will be k=[b][a].

increasing the concentration of a will result in the formation of excess b. thus, the equilibrium shifts to the product side, and the concentration of b increases.

if the equilibrium shifts toward the product side of the reaction, then the formation of the product is favored, and if equilibrium shifts toward the reactant side of the reaction, then the formation of the reactant is favored.