How does Le Chatelier's principle explain the result you obtained when you add HCL to a suspension of Ca(OH)2 in water? Where the result was, precipitate dissappeared and an increase in temperature resulted.
Ca(OH)2 solid in H2O. Saturated solution.
Ca(OH)2 + 2HCl ==> CaCl2 + H2O
Ca(OH)2 suspension. Saturated solution. Add HCl. The New ionic rxn is
2OH^- + 2H^+ ==> 2H2O. H2O is very weak electrolyte. Rxn goes to completion forming H2O. That reduces the OH^- in solution forcing more of the solid to dissolve. More HCl does the same thing; eventually all of the lime has dissolved. The temperature increases because H^+ + OH^- ==> H2O + heat; i.e., an exothermic reaction.
Le Chatelier's principle states that when a system in equilibrium is disturbed by changes in temperature, pressure, or concentration of reactants or products, the system will respond to counteract the change and restore equilibrium.
In the case of adding HCl to a suspension of Ca(OH)2 in water, HCl is a strong acid that dissociates completely into H+ ions and Cl- ions in water. Ca(OH)2 is a strong base that also dissociates completely into Ca2+ ions and OH- ions in water. The reaction between HCl and Ca(OH)2 can be represented as follows:
2HCl + Ca(OH)2 → CaCl2 + 2H2O
Initially, when HCl is added to the suspension of Ca(OH)2, the H+ ions from the acid react with the OH- ions from the base to form water. This reaction uses up the OH- ions, which leads to a decrease in the concentration of OH- ions in the suspension. As a result, the equilibrium is disturbed as the concentration of OH- ions is lowered.
According to Le Chatelier's principle, the system will shift in a direction that minimizes the disturbance caused. In this case, the system will shift to replenish the OH- ions that were consumed. One way to do this is by dissolving more Ca(OH)2 to produce more OH- ions. As a result, the precipitate formed by the reaction between Ca2+ ions and OH- ions dissolves, and the solution becomes clear.
In addition to the disappearance of the precipitate, an increase in temperature is also observed. This can be explained by considering the reaction between HCl and Ca(OH)2. The reaction is exothermic, meaning it releases heat. When the equilibrium is disturbed by adding HCl, the forward reaction (formation of CaCl2 and water) is favored to counteract the disturbance. Since the forward reaction is exothermic, its progress releases more heat, leading to an increase in temperature.
So, Le Chatelier's principle explains the disappearance of the precipitate and the increase in temperature when HCl is added to a suspension of Ca(OH)2 in water. By understanding the principles behind this, you can predict how equilibrium systems will respond to various disturbances.