Effect Of Change In Temperature And Presence Of Catalyst On Equilibrium

Le Chatelier's principle can be used to predict the effect of temperature on the equilibrium of a reaction.

Whenever a system at equilibrium is subjected to change in concentration or pressure, then

Qc ≠ Kc

However, when a system at equilibrium is subjected to change in temperature, the value of equilibrium constant Kc itself changes.

The value of the equilibrium constant for a given reaction varies with temperature. In general:

a) Equilibria in which the forward reaction is exothermic, where the enthalpy change is negative, have equilibrium constants that decrease with an increase in temperature.

b) Equilibria in which the forward reaction is endothermic, where the enthalpy change is positive, have equilibrium constants that increase with an increase in temperature.

For an endothermic reaction, with an increase in temperature, the value of equilibrium constant Kc also increases.

Lowering the temperature for an exothermic reaction favours the backward reaction. A catalyst has no effect either on the position of equilibrium or on the equilibrium composition of a reaction mixture.

However, a catalyst increases the rate of the reaction by providing a new low-energy pathway for the conversion of the reactants into products.

A catalyst lowers the activation energy for the forward as well as the reverse reaction by exactly the same amount thus, makes it easy for the reaction to proceed faster in either direction.

Summary

Le Chatelier's principle can be used to predict the effect of temperature on the equilibrium of a reaction.

Whenever a system at equilibrium is subjected to change in concentration or pressure, then

Qc ≠ Kc

However, when a system at equilibrium is subjected to change in temperature, the value of equilibrium constant Kc itself changes.

The value of the equilibrium constant for a given reaction varies with temperature. In general:

a) Equilibria in which the forward reaction is exothermic, where the enthalpy change is negative, have equilibrium constants that decrease with an increase in temperature.

b) Equilibria in which the forward reaction is endothermic, where the enthalpy change is positive, have equilibrium constants that increase with an increase in temperature.

For an endothermic reaction, with an increase in temperature, the value of equilibrium constant Kc also increases.

Lowering the temperature for an exothermic reaction favours the backward reaction. A catalyst has no effect either on the position of equilibrium or on the equilibrium composition of a reaction mixture.

However, a catalyst increases the rate of the reaction by providing a new low-energy pathway for the conversion of the reactants into products.

A catalyst lowers the activation energy for the forward as well as the reverse reaction by exactly the same amount thus, makes it easy for the reaction to proceed faster in either direction.

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