State law of mass action. [2]

The Law of Mass Action states that:

The rate of a chemical reaction is directly proportional to the product of the active masses of the reacting substances, each raised to the power of their respective stoichiometric coefficients in the balanced chemical equation.

Mathematically, for a general reaction: $$aA+bB\rightleftharpoons cC+dD$$

The equilibrium constant expression is: $$K_c=\frac{[C{]}^c[D{]}^d}{[A{]}^a[B{]}^b}$$ where:

• $[A]$, $[B]$, $[C]$, and $[D]$ are the molar concentrations of the reactants and products at equilibrium.
• $a$, $b$, $c$, and $d$ are the stoichiometric coefficients.
• $K_c$ is the equilibrium constant in terms of concentration.

This law applies only to gases and solutions, where concentrations can be expressed in terms of molarity. For gases, partial pressures are used instead of concentrations, denoted as $K_p$.