Saturday, 15 June 2013

Law stating that the rate of any chemical reaction is proportional to the product of the masses of the
reacting substances, with each mass raised to a power equal to the coefficient that occurs in the chemical equation. This law was formulated over the period 1864–79 by the Norwegian scientists Cato M. Guldberg and Peter Waage but is now of only historical interest. This law was useful for obtaining the correct equilibrium equation for a reaction, but the rate expressions it provides are now known to apply only to elementary reactions. By the term active mass we mean the molar concentration,or number of moles per dm3 in a dilute solution.

a A + b B --> c C + d Dwhere a, b, c, d are the coefficients for a balanced chemical equation.

The mass action law states that if the system is at equilibrium at a given temperature, then the following ratio is a constant.

[C]c [D]d
------------- = Keq
[A]a [B]b

The square brackets "[ ]" around the chemical species represent their concentrations. This is the ideal law of chemical equilibrium or law of mass action.The units for K depend upon the units used for concentrations. If M is used for all concentrations, K has units


Accordin to law of Mass Action

the rate of forward reaction is proportional to [A] [B],while the rate of reserve reaction is equal to kr [C] [D] where kf and kr are the rate of constant for the forward and reverse reactions,respectively

Law of Mass Action


  1. Hey Zaibi its very nice post and i got too much help