Notes On Equilibrium Constant: Characteristics - CBSE Class 11 Chemistry
Equilibrium in a system having two (or) more phases is known as heterogeneous equilibrium. Heterogeneous equilibria often involve pure solids (or) liquids. Consider the thermal decomposition of calcium carbonate in a closed vessel, the equilibrium constant for this reaction can be written as CaCO3(s) ${\text{CaO}}_{\text{(S)}}$${\text{CO}}_{\text{2}}$ Kc = $\frac{\text{[CaO][}{\text{CO}}_{\text{2}}\text{]}}{\text{[}{\text{CaCO}}_{\text{3}}\text{]}}$ Since calcium carbonate and calcium oxide are solids, their concentrations remain constant, and hence, their concentration terms in the expression for equilibrium constant can be ignored. K'c = [CO2] or Kp = pCO2 It shows that at a particular temperature, irrespective of the masses of the two solids Calcium oxide and Calcium carbonate, there is a constant concentration or pressure of Carbon dioxide in equilibrium with calcium oxide and calcium carbonate. Characteristics of equilibrium: The value of equilibrium constant is independent of the initial concentrations of the reactants and products. The equilibrium constant for a particular reaction at a particular temperature is always constant and changes only with a change in temperature. The equilibrium constants of a forward reaction and its backward reaction are reciprocals of each other. If a chemical equation is multiplied by a certain factor, then its equilibrium constant must be raised to a power equal to that factor in order to obtain the equilibrium constant for the new reaction.

#### Summary

Equilibrium in a system having two (or) more phases is known as heterogeneous equilibrium. Heterogeneous equilibria often involve pure solids (or) liquids. Consider the thermal decomposition of calcium carbonate in a closed vessel, the equilibrium constant for this reaction can be written as CaCO3(s) ${\text{CaO}}_{\text{(S)}}$${\text{CO}}_{\text{2}}$ Kc = $\frac{\text{[CaO][}{\text{CO}}_{\text{2}}\text{]}}{\text{[}{\text{CaCO}}_{\text{3}}\text{]}}$ Since calcium carbonate and calcium oxide are solids, their concentrations remain constant, and hence, their concentration terms in the expression for equilibrium constant can be ignored. K'c = [CO2] or Kp = pCO2 It shows that at a particular temperature, irrespective of the masses of the two solids Calcium oxide and Calcium carbonate, there is a constant concentration or pressure of Carbon dioxide in equilibrium with calcium oxide and calcium carbonate. Characteristics of equilibrium: The value of equilibrium constant is independent of the initial concentrations of the reactants and products. The equilibrium constant for a particular reaction at a particular temperature is always constant and changes only with a change in temperature. The equilibrium constants of a forward reaction and its backward reaction are reciprocals of each other. If a chemical equation is multiplied by a certain factor, then its equilibrium constant must be raised to a power equal to that factor in order to obtain the equilibrium constant for the new reaction.

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