Very carefully, but breifly discuss, with specific example, Le Chatelier Principle and its relationship to common ion effect.
The Le Chatelier Principle is a fundamental concept in chemistry that states that when a system at equilibrium is disturbed by a change in conditions, the system will respond by shifting in a direction that counteracts the disturbance. In other words, if any change is applied to a system in equilibrium, the system will adjust to minimize the impact of that change and restore equilibrium.
The common ion effect is a specific application of the Le Chatelier Principle. It occurs when a soluble compound is dissolved in a solution that already contains one of its constituent ions. This presence of a common ion reduces the solubility or dissociation of the compound, shifting the equilibrium towards the formation of more of the undissociated compound.
To better understand this, let's consider the example of the dissolution of calcium fluoride (CaF2) in water. When CaF2 is added to water, it dissociates into its constituent ions: Ca^2+ and 2F^-. At equilibrium, some of the CaF2 remains undissociated, while dissociated ions are also present in solution.
Now, let's say we add some sodium fluoride (NaF) to the solution. Sodium fluoride also contains the same fluoride ion (F^-) as calcium fluoride. As a result, the concentration of the fluoride ion in the solution increases due to the additional F^- ions from NaF.
According to the Le Chatelier Principle, the system will respond to this increase in fluoride ion concentration by shifting the equilibrium to the left, favoring the formation of more undissociated CaF2. This decrease in the dissociation of CaF2 is the common ion effect.
As a result of the common ion effect, the solubility of calcium fluoride decreases in the presence of a common ion (fluoride ion in this case). This phenomenon can be observed in various other chemical equilibria involving common ions.
In summary, the Le Chatelier Principle states that a system at equilibrium will respond to a disturbance by shifting in a direction that reduces the impact of the disturbance. The common ion effect is a specific application of this principle, where the presence of a common ion reduces the solubility or dissociation of a compound in a solution.