### Principle of Chemical equilibrium:

- This theory was proposed by
*Goldberg*and*Waage*in 1884. - According to this law ,rate of reaction at a given temperature is directly proportional to the product of active masses of the reactants, raised to the power equal to stoichiometric co- efficient of the balanced chemical equation at a particular instant of reaction.
- It explains and predicts the behaviour of solution in dynamic equilibrium.
- Specifically it implies that for a chemical reaction reaction mixture in equilibrium, the ratio between concentration of reactants and products is constant.

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Derivation of equilibrium constant in terms of concentration:* *

Consider a hypothetical reversible reaction i.e.

aA(g) + bB(g) ⇔ cC(g) + dD(g)

Applying law of mass action here,

[A], [B], [C] and [D] being the active masses

k

a, b, c, d are the stoichiometric coefficients related to A, B, C and D respectively. However, at the equilibrium ,

Rate of forward reaction = Rate of backward ,

or,

or,

or,

or,

Applying law of mass action here,

- Rate of forward reaction would be k
[A]_{f }^{a}[B]^{b}^{} - Rate of backward reaction would be k
[C]_{b }^{c}[D]^{d}^{ }

[A], [B], [C] and [D] being the active masses

k

_{f}and k_{b}are rate constants of forward and backward reactions,a, b, c, d are the stoichiometric coefficients related to A, B, C and D respectively. However, at the equilibrium ,

Rate of forward reaction = Rate of backward ,

or,

or,

or,

or,

*K*_{eq}= K_{f}/ K_{b }_{}Where K_{c }is known as equilibrium constant(if concentration is given).
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