K_(ep) is the equilibrium product constant. It determines what you have more of, or what is "favored". If K_(eq) is less than one, you have more reactants. If it is greater than 1 you have more products.
K_(eq) is calculated by taking the concentration of the products divided by the concentration of the reactants.
For the balanced reaction:
aA + bB -> cC + dD
the equilibrium constant, K_(eq )is:
K_(eq) = ([C]^c*[D]^d)/([A]^a*[B]^b)
the above example is from: http://www.chemicool.com/
Note that the coefficients become exponents.
Also know that concentrations are never added or subtracted, only multiplied and divided.
The unit for concentration is usually moles/liter (Molarity)
