Many reactions will reach equilibrium. Theoretically all reactions will eventually reach equilibrium. If a reaction is in equilibrium, no net changes are observed. Equilibrium is dynamic, but the ratio of the product to reactant concentrations remain constant. So, how would a chemical manufacturer make money if this is the case? Well, according to Le Chatelier’s Principle:

 
A disturbance can be a change in concentration, a temperature change, or a change in pressure by increasing or decreasing the volume of the system at equilibrium. In simple terms, if something is added to the system, it will shift in such a way to remove what has been added. If something is removed from the system, it will shift to replace what has been removed. Recall the value of the equilibrium constant is constant at a constant temperature. A change in temperature is the only parameter that will change the equilibrium constant.

Chemical manufacturers are able to manipulate systems at equilibrium to produce a higher yield of product. In the following sections, we will discuss these methods.

Effects of Changes in Concentration

Consider the following reaction at equilibrium:

If more H₂S or O₂ is added, the system will shift to the right to counteract the change. If either H₂S or O₂ is removed, the system will shift to the left to counteract the change. To see why this occurs, we will look at the equilibrium constant expression below.

A change in concentration, at a constant temperature, does not affect the equilibrium constant. If we add more H₂S, the system will need to shift to the right until