Knowledge database: Chemical equilibrium: Equilibrium constant

The chemical equilibrium constant is a numeric value that shows us the extent to which a particular reaction is carried out. Many reactions that we often face are carried out almost to the end, which means that almost all reactants are turned into products. This however is not always the case. There are cases when the reaction stops before all the reactants are used, so as a result of the reaction we don't only have the products, but we also have some of the remaining reactants.

The chemical equilibrium constant is symbolized by the letter K, and can be calculated by multiplying the molar concentrations of products (raised to the power of their stoichiometric coefficients), and dividing the result by the multiplied molar concentrations of reactants (also raised to the power of their stoichiometric coefficients).

If we look at the chemical equation to the left in the picture above, we see that A, B, C and D are different reactants (and products), while n, m, p and q are the values of stoichiometric coefficients. On the right side we can see the formula for calculating the chemical equilibrium constant from the variables listed in the chemical equation.

The values of the chemical equilibrium constants around 0.01 or less indicate that the equilibrium is shifted to the left (very little amount of products is obtained). Values between 0.01 and 100 are in the balanced range, and in this case, there are considerable amounts of both, reactants and products present. Finally, the values above 100 indicate that the equilibrium is shifted to the right, which means that such reactions carry out almost completely and only a very small amount of reactants is left unreacted.