Representation of the Equilibrium Constant
For a chemical reaction that is represented by the following equation,
aA + bB → cC + dD
Equilibrium Constant (Kc) expression is written as follows,
Kc = [C]c[D]d/[A]a[B]b
Kc is related to concentrations of reactants and products. In a similar expression, when partial pressures of the gaseous components is substituted, it becomes Kp and when mole fractions are substituted, it is called Kx, i.e.
Kp = pAa.pBb/pCcpDd
Kx = [XC]c[XD]d/[XA]a[XB]b
Relation between Kc, Kp and Kx
The relation between Kp and Kc is given as,
Kp = Kc (RT)Δng
where,
- Kc = equilibrium constant,
- Kp = equilibrium constant in terms of partial pressures
- R = gas constant
- T = temperature
- Δng = number of gaseous components in products – number of gaseous components in reactants
And, the relation between Kx and Kc is given as,
Kx = Kc(RT/pT)Δng
where,
- Kc = equilibrium constant,
- Kx = equilibrium constant in terms of mole fractions,
- R = gas constant,
- T = temperature,
- pT = total pressure,
- Δng = number of gaseous components in products – number of gaseous components in reactants
Law of Mass Action
Law of Mass Action relates to the rate of a chemical reaction. It states that the rate of a reaction is directly proportional to the concentrations of its reactants. More precisely, the rate of a chemical reaction is directly proportional to the product of its reactant concentrations raised to their respective stoichiometric coefficients at constant temperature and pressure. This implies that an increase in reactant concentration would lead the reaction to move forward at a faster rate. The law of mass action forms the basis for equilibrium constant expression, which helps in quantifying the dynamics of the reaction.
In this article, we will discuss what is meant by the Law of Mass Action, Equilibrium Constant, Chemical Equilibrium, applications of the law and related frequently asked questions.