Factors Affecting Equilibrium State

The state of equilibrium is in a dynamic balance between forward and backward reaction. This balance can be disturbed by changing concentration, temperature or pressure. If done so a certain net change occurs in the system. The direction of change can be predicted with the help of Le-Chatelier principle.

Le Chatelier Principle

It states that when a system in equilibrium is disturbed by a change in concentration, pressure or temperature, a net change occurs in it in a direction that tends to decrease the disturbing factor.

Change in Concentration

When the concentration of reactant is increased, a net forward reaction will take place which consumes the added reactant. If the concentration of product is increased, a net backward reaction would take place to utilize the added product.

Change in Pressure

Change in pressure affects equilibrium involving gaseous phase either in a homogeneous or hetrogeneons system. 

When the number of moles of products is more than the total number of moles of reactants, increase in total pressure keeping the temperature constant, will cause a decrease in volume. This means that the number of moles per unit volume will increase. A net change will take place in the equilibrium in the direction where the number of moles decrease i.e. backward direction.

When the number of moles of products is less than reactants, increase in total pressure will bring a net change to the equilibrium in the direction where the total number of moles is decreasing i.e. to the product side. Decrease in total pressure will bring the net change to equilibrium in the direction where the total number of moles is increasing i.e. backward direction.

When there is no change in the total number of moles of reactant and product, there is no net change in equilibrium state when pressure is changed.

Change of Temperature

According to Le Chatelier prinicple when the temperature is changed (increased or decreased) the equilibrium system reacts to nullify the change in heat content. However, the net change in equilibrium is directed by the exothermic or endothermic nature of reaction.

For the system of equilibrium of exothermic reaction, according to Le Chatelier priniciple increase in temperature brings a net change in the equilibrium state in that direction where this extra heat is consumed. The net change is in the backward direction. Similarly if the temperature is decreased the equilibrium shifts to the forward direction.

For endothermic reaction, if the temperature is increased the added heat will be absorbed by the reactant and the net change takes place to the equilibrium in the forward direction. If the temperature is decreased it will bring a net change to equilibrium in the backward direction i.e. direction in which it is exothermic.

Addition of a Catalyst

It does not affect the equilibrium. However, it helps to achieve the equilibrium faster.