Why does not the equilibrium position change when solids or liquids are added to a solution at equilibrium ?..m really confused!..
Changing the amount of one of the reaction components can affect the equilibrium only if the concentration of that component is changed. The concentration of a component depends on the ratio of the amount of that component (moles) to the total amount of that phase (usually the volume of the phase, but other quantities such as the total number of moles or the mass of solvent in that phase may also be used). The addition of a pure solid or a pure liquid does not usually change the concentration of that component, since both the number of moles of that component and the total amount of that phase are both changed by the same factor.
Therefore, the addition of a pure solid component to a system at constant pressure has no effect on the amounts of the other components. However, the addition of a liquid which is a solvent for one of the phases may have a secondary effect by lowering the concentrations of all of the reaction components dissolved in that phase. The addition of a substantial amount of liquid or solid to a container at constant volume may also have a secondary effect of compressing the gaseous phase, thus increasing the concentrations of all gaseous compounds.