How much HCl is made? We start with zero, but we also see that 2 mol of HCl are made for every mole of H 2 (or Cl 2) that reacts (from the coefficients in the balanced chemical equation), so if we lose x M H 2, we gain 2 x M HCl. If we start with 1.0 M Cl 2 at the beginning and we react x M, we have (1.0 − x) M Cl 2 left at equilibrium. This means that if x M H 2 reacts, x M Cl 2 reacts as well. How do we know that? The coefficients of these two species in the balanced chemical equation are 1 (unwritten, of course).

This means that at equilibrium, we have (1.0 − x) M H 2 left over.Īccording to the balanced chemical equation, H 2 and Cl 2 react in a 1:1 ratio. Let us assume that x M H 2 reacts as the reaction goes to equilibrium. But by how much will it proceed? We don’t know, so let us assign it a variable. Its associated K eq is 4.0, and the initial concentration of each reactant is 1.0 M:īecause we have concentrations for the reactants but not the products, we presume that the reaction will proceed in the forward direction to make products. Such calculations are not difficult to do, especially if a consistent approach is applied.

There are some circumstances in which, given some initial amounts and the K eq, you will have to determine the concentrations of all species when equilibrium is achieved. Calculate equilibrium concentrations from the values of the initial amounts and the K eq.

How to calculate keq