Knowledge database: 5.1 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 reactants are used, so as a result of the reaction we don't only have products, but we also have some of the remaining reactants.

The chemical equilibrium constant is symbolized by K, and can be calculated by multiplying the molar concentrations of products (squared by their values of stoichiometric coefficients), and dividing the result by the multiplied molar concentrations of reactants (also squared by values 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 reaction balance is more on the side of reactants (very little amount of products is produced). 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 reaction balance is significantly placed on the side of products, and therefore the reaction will carry out almost completely and only very small amount of reactants will be left unreacted.