Consider the following reaction. CaO (s) + H2O (l) Ca(OH)2 (s) + 65.2 kJ
If you start with a container holding a mixture of the CaO (s), H2O (l) and Ca(OH)2 (s) at equilibrium, describe what happens to the amount of CaO if each of the following changes was made to the original sample?
a. The mixture is heated.
b. H2O (l) is added to the mixture.
c. Ca(OH)2 is removed from the mixture.
d. The mixture is cooled.
This is a question involving Le Chatelier's Principle. That Principle says it so beautifully if you write it out but most students don't get it. So here is a country boy's take on it in very simple words.
In a system at equilibrium, the equilibrium will shift so as to undo what we do to the reaction in order to reach a new equilibrium under the new conditions. CaO (s) + H2O (l) ==> Ca(OH)2 (s) + 65.2 kJ
Now let's rewrite it since 65.2kJ is heat to
CaO (s) + H2O (l) ==> Ca(OH)2 (s) + heat.
I'll do the first two. You do the last two.
a. The mixture is heated.
So the reaction gives off heat. If we heat the mixture at equilibrium, it will shift (move to the right or to the left) so as to undo what we did. So if we are adding heat it will move to the left because it doesn't want to add more heat So solid CaO will increase. The problem doesn't ask but liquid water will increase also and solid Ca(OH)2 will decrease.
b. H2O (l) is added to the mixture.
Adding H2O will make the equilibrium shift to the right so CaO will decrease, Ca(OH)2 will increase and more heat will be generated.
c. Ca(OH)2 is removed from the mixture.
d. The mixture is cooled.
I shall be happy to check your answers for c and d.
a. If the mixture is heated, according to Le Chatelier's principle, the reaction will shift in the direction that consumes heat in order to counteract the increase in temperature. In this case, the forward reaction is exothermic, meaning it releases heat, so an increase in temperature will shift the reaction towards the left, favoring the reverse reaction. As a result, some of the CaO will be converted into Ca(OH)2, causing the amount of CaO to decrease.
b. If H2O (l) is added to the mixture, it will increase the concentration of the reactant on the right side of the equation. According to Le Chatelier's principle, the reaction will shift in the direction that consumes the excess reactant in order to re-establish equilibrium. In this case, it will shift towards the left, causing some of the Ca(OH)2 to react and form CaO. Therefore, the amount of CaO will increase.
c. If Ca(OH)2 is removed from the mixture, it will decrease the concentration of the product on the right side of the equation. According to Le Chatelier's principle, the reaction will shift in the direction that produces more of the reactant in order to compensate for the decrease. In this case, it will shift towards the right, causing more CaO to react and form Ca(OH)2. As a result, the amount of CaO will decrease.
d. If the mixture is cooled, the reaction will shift in the direction that generates heat in order to maintain the temperature. In this case, the forward reaction is exothermic, so a decrease in temperature will shift the reaction towards the right, favoring the forward reaction. As a result, more Ca(OH)2 will react to form CaO, causing the amount of CaO to increase.
a. If the mixture is heated, it will cause an increase in temperature. According to Le Chatelier's principle, when a system at equilibrium is subjected to a change in temperature, the system will react in a way that counteracts the change. In this case, the reaction is exothermic, meaning it releases heat. Thus, an increase in temperature will cause the reaction to shift towards the left, or in reverse, to consume some of the excess heat. As a result, the amount of CaO will decrease in order to restore equilibrium.
b. If additional H2O (l) is added to the mixture, it will increase the concentration of water in the system. Following Le Chatelier's principle, the system will respond by shifting in the direction that reduces the concentration of water. In this case, it means that the reaction will shift towards the right, or forward, to consume the excess water. Consequently, the amount of CaO will decrease as it is consumed to generate more Ca(OH)2.
c. If Ca(OH)2 is removed from the mixture, it disrupts the equilibrium by decreasing the concentration of the product. As a response to the decrease in Ca(OH)2, the system will shift towards the right, or forward, to reestablish equilibrium. This means that more CaO will react with the remaining water to produce more Ca(OH)2. Therefore, the amount of CaO will decrease.
d. When the mixture is cooled, it will cause a decrease in temperature. According to Le Chatelier's principle, the system will react in a way that counteracts the change. For an exothermic reaction, a decrease in temperature will cause the reaction to shift towards the direction that generates more heat. In this case, the reaction will shift towards the right, or forward, to increase the production of Ca(OH)2 and release more heat. Hence, the amount of CaO will decrease as it is consumed to generate more Ca(OH)2.