At a constant temperature, the rate of a chemical reaction is directly proportional to the product of the molar concentrations of the reactants each raised to a power equal to the corresponding stoichiometric coefficients as represented by the **balanced chemical equation.** Let us consider the reaction,

aA + bB +… ⟶ products

Rate of reaction α [A]^{a}[B]^{b}……

By the law, rate of reaction = k[A]^{a}[B]^{b}…

Here a and b are stoichiometric coefficients. K is the rate constant.

Let us consider a general reversible reaction

A + B ⇌ C + D

Applying **Law of Mass Action**,

Rate of the forward reaction α[A][B] = K_{f}[A][B]

When K_{f} is a constant of proportionality and is called **velocity constant** for the forward reaction.

Rate of the backward reaction α[C][D] = K_{b}[C][D]

At equilibrium,

Rate of the forward reaction = Rate of the backward reaction

At constant temperatures K is also constant and is called **Equilibrium constant**.

Now let us consider a more general reversible reaction in a state of equilibrium. By applying Law of mass action.

## Equilibrium Constant for the reaction

## Relationship between Equilibrium constant K, reaction Quotient Q and Gibbs energy G.

A mathematical expression of thermodynamic view of equilibrium can be described by time equation.

where G^{⊖} is standard Gibbs energy.

At equilibrium when ∆G = 0

Taking antilog on both sides