Massenwirkungs-Gesetz?

You know, however, how the Mass Effects Act looks:

In addition, initial concentrations are given for all three substances, and it is required in which direction the reaction will take place. You simply put the three concentrations in the expression; since the system is not in equilibrium, you do not get the equilibrium constant K=36.9 l/mol, but a small number Q=208 l/mol. The number is too large (Q>K), so the reaction will run backwards (SO3 decays to SO2 and O2) until the correct value is reached (Q=K).

We can even calculate which concentrations will be adjusted. To this end, we consider that for each disintegrated SO3 molecule an SO2 molecule and half an O2 molecule are formed. Thus, if x SO3 molecules decompose, the SO2 or O2 concentrations increase by x or x/2.

We write this into the Mass Effects Act

where the c0 is the initial concentrations mentioned in the specification. This equation can be dissolved after x and x=0.027157 mol/l. The following concentrations are thus obtained for equilibrium: c(SO3)=0.0978 mol/l, c(SO2)=0.0772 mol/l and c(O2)=0.0436 mol/l.