The molar equilibrium constant (Kc) is a measure of the extent of a chemical reaction at equilibrium. It is defined as the ratio of the concentrations of the products to the concentrations of the reactants, with each concentration raised to the power of its stoichiometric coefficient:
Kc = [C]^c[D]^d/[A]^a[B]^b
where A, B, C, and D are the reactants and products of the chemical reaction, and a, b, c, and d are their respective stoichiometric coefficients.
The molar equilibrium constant is different from the regular equilibrium constant (Keq) in that Keq is expressed in terms of the activities of the reactants and products, rather than their concentrations. Activities take into account the effects of temperature, pressure, and other factors on the reactivity of the species involved in the reaction, while concentrations do not.
The relationship between Kc and Keq can be expressed as:
Kc = Keq(RT)^Δn
where R is the gas constant, T is the temperature in Kelvin, and Δn is the difference between the total number of moles of gaseous products and the total number of moles of gaseous reactants.
In summary, the molar equilibrium constant (Kc) is a measure of the extent of a chemical reaction at equilibrium, expressed as the ratio of the concentrations of the products to the concentrations of the reactants. It differs from the regular equilibrium constant (Keq) in that Keq is expressed in terms of the activities of the species involved in the reaction, and takes into account the effects of temperature, pressure, and other factors on reactivity.