The symbol for the Equilibrium Constant is K_eq.

To find the equilibrium constant, you use the equilibrium constant expression. The rule for the equilibrium constant expression is as follows:

For the following reaction at equilibrium:

aA+bB <=> cC + dD

The Equilibrium Constant Expression is:

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

In other words, it is the concentrations of the products over the concentrations of the reactants, with each element being raised to the power of its coefficient.