Factors Affecting the Equilibrium (Le-Chatelier Principle):
According to Le-Chatelier principle, if a system at equilibrium is subjected to change in any of the factors that determine such as pressure, temperature, or concentration, then, the equilibrium shifts in such a manner as to reduce or to counteract the effect of the change.
The principle is very helpful in predicting the effect of change in concentration, pressure or temperature on a system in equilibrium. Let us apply Le-Chatelier principle to explain the effect of changes in concentration, temperature and pressure on various reactions on equilibrium.
i) Effect of change of concentration:
According to Le-Chatelier principle, if concentration of one or all the reactant species is increased, the equilibrium shifts in the forward direction and more of products are formed. Therefore, increase in concentration of any of the reactant shifts the equilibrium to forward direction and increase in concentration of any of the products shifts the equilibrium to backward direction.
ii) Effect of change of Temperature:
According to Le-Chatelier principle, an increase in temperature favours forward reaction in endothermic process. In exothermic process, low temperature is favourable for forward reaction.
iii) Effect of change of Pressure:
According to Le-Chatelier principle, an increase of pressure on a system at equilibrium will shift the equilibrium in the direction in which pressure is reduced. If the pressure of a gaseous system is increased the volume occupied by the system decreases so that total number of moles per unit volume increases. To undo this stress, the reaction which produces small number of moles of gaseous substance will be favoured so that the increased pressure is reduced. Thus, increase in pressure will favour the backward reaction.
iv) Effect of change of volume:
we know that increase in pressure means decrease in volume, therefore the effect of change of volume will be exactly reverse to that of pressure.
v) Effect of Catalyst: – Catalyst has no effect on equilibrium.