Homogeneous equilibrium

Homogeneous equilibrium

 In a homogeneous system, all the reactants and products are in the same phase. For example, in the gaseous reaction,
N2(g) + 3H2(g)
 2NH3(g), reactants and products are in the homogeneous phase. Similarly, for the reactions,

CH3COOC2H5 (aq) + H2O (l)  CH3COOH (aq) + C2H5OH (aq)

and, Fe3+ (aq) + SCN(aq)  Fe(SCN)2+ (aq)

all the reactants and products are in homogeneous solution phase.

Equilibrium Constant in Gaseous Systems

 In case of gases their partial pressures can also be used in place of molar concentrations (since the two are directly proportional to each other) in the law of equilibrium. The new equilibrium constant, Kp, is called the pressure equilibrium constant. For the reaction between H2 and I2 ,Kp is given by

Relation between Kp and Kc

 

For a general gas phase reaction at equilibrium

The pressure and concentration equilibrium constants Kp and Kc are

For a gaseous substance i, the ideal gas equation is

 

Units of Equilibrium Constant

 Units of equilibrium constant Kc or K p depend upon the fact whether during the reactions there is any change in the moles of substance or not

(b) The reaction where there is change in the moles of substance i.e.Δn ≠ 0.