Question

$When in any system at equilibrium state pressure, temperature and concentration are changed then the equilibria shifted to such a direction that neutralizes the effect of change. This is known as [MP PMT/PET$1988$; DPMT$1985$]
A. First law of thermodynamics
B. Le-chatelier’s principle
C. Ostwald’s rule
D. Hess’s law of constant heat summation

Answer 1

Hint: A chemical system when it is at equilibrium is disturbed by pressure, temperature, and concentration, and then the equilibrium condition of the system is altered. The overall reaction will take place in the same direction until a new equilibrium state is achieved.

Complete answer:The term ‘equilibrium’ indicates the reaction conditions where the rate of forward reaction of product formation is equal to the rate of backward reaction of reactant formation. As a result, the interchange of reactants and products is constant. Even when the forward and backward reactions are occurring simultaneously, the concentrations of all chemical species in the system remain constant.

The behavior of any system at equilibrium follows Le-Chatelier’s principle. According to Le-Chatelier’s principle when any system at equilibrium state pressure, temperature, and concentration is changed then the equilibria shifted in such a direction that neutralizes the effect of change.

When the pressure changes in any system: If pressure increases at equilibrium the reaction will shift towards the direction with lower pressure or if the pressure decreases the reaction will shift towards the direction with higher pressure.

When temperature changes of any system: At equilibrium when temperature increases, the heat of the system increases, and the system will shift towards the reactant side where heat is absorbed. When the temperature decreases, the heat of the system decreases, and the system will shift toward the product side where heat is released.

When concentration changes in any system: An increase in the concentration of reactant will shift towards more product concentration and with increasing the concentration of product the system will shift the equilibrium towards more reactant concentration.

Thus, option (B) is correct.

Note: At equilibrium when inert gas is added, the net pressure of the system will increase but the concentration of reactants and products will be unaffected in that condition. When at constant pressure inert gas is added the net volume will increase but the number of moles per unit volume of reactants and products will decrease.