Homogenous and heterogeneous equilibrium

  • Expression for the equilibrium constant of a reaction is written in the form of a ratio. The numerator consists of the molar concentration (or partial pressure) terms of the products each raised to a power equal to its stoichiometric coefficient in the balanced chemical equation, and the denominator consists of the molar concentration (or partial pressure) terms of the reactants each raised to a power equal to the stoichiometric coefficient in the balanced chemical equation.

Equilibrium in which all the reactants and products are in the same phase is called homogeneous equilibrium reaction. For example,

example for homogeneous equilibrium reaction

  • The concentration term of the solvent, which is present in large excess is not included in the equilibrium constant expression.

For example, for the reaction,

The equilibrium constant may be written as:

By convention we write [H2O] = constant so that,

The [H2O] term is merged with the equilibrium constant.

  • Equilibrium reactions in which the reactants and products are present in different phases are called heterogeneous equilibrium reactions.

example for heterogeneous equilibrium reaction

example for heterogeneous equilibrium reaction

For heterogeneous reactions, the concentration terms for pure solids and pure liquids are not included in the expression for equilibrium constant. The concentration of pure solids and liquids remain constant, and these terms are merged into the equilibrium constant or by convention their concentrations are taken as unity, i.e., [solid] = 1, [liquid] = 1.

For example, the equilibrium constant for the reaction,

By convention [Fe(s)] = 1 and [Fe3O4(g)] = 1,

so the equilibrium constant is,

For the reaction,

The equilibrium constant is,

Ksp = [Ag+(aq)] [Cl-(aq)]

The constant for this reaction is called solubility product constant (Ksp).

Problem

7. Classify each of the following equilibrium as homogeneous or heterogeneous:

Solution

(i) Homogeneous

(ii) Heterogeneous

5 comments:

mcarrington said...

Hi,
How do you deal with reactions containing solutions and gases, both of which can be expressed as concentrations, but in different solvents?
For example: CO2(g) + H2O(l) <-> HCO3-(aq) + H+(aq)

Unknown said...

Agen togel Terpercaya

math

Unknown said...

Agen togel Terpercaya

loverr

Anonymous said...

if reactants and products aee in same phase but having catalyst in diff phase.such as in haber process.then what we call that equilibrium.
homo or hetero?

Anonymous said...

you welcome