If we change the concentration of either reactants or products, the value of equilibrium constant also changes. Suppose you have an equilibrium established between four substances A, B, C and D
Let's say we decrease the concentration of 'C', technically the value of will reduce according to the above expression. But, if you know Le Chatelier's principle, it states that when a system experiences a disturbance (such as concentration, temperature, or pressure changes), it will respond to restore a new equilibrium state. This means that the system subjected to a change will try to move in a direction that reduces the effect of the change (image below). When all this takes place, the value of does not change.