Indicate how the concentration of each species in the chemical equation will change to reestablish equilibrium after a decrease in pressure or volume.

The change in the concentration of the substances in a system to reach equilbrium after changing certain factors like pressure and volume can be explained by the Le Chatelier's Principle. One example would be if you have a system where one of the product is a gas, increasing the pressure would shift the equilibrium towards the formation of the reactants.