PCl5 --> PCl3 + Cl2 (Kp = 630 at 546 K)
A system is prepared by placing equimolar amounts of the three gases shown in the equation above in a suitable rigid container held at constant volume. Equilibrium is established at 546 K.
(A) When equilibrium is established, how does [PCl3] compare to [Cl2]? Explain.
(B) When equilibrium is established, how does [PCl5} compare to [PCl3]? Explain.
(C) When equilibrium is established, how does the rate of the forward reaction compare to the rate of the reverse reaction? Explain.
(D) If the volume of the container is increased at constant temperature, then:
(1) What effect is observed on the number of moles of PCl5 in the system? Explain.
(2) Does the value of Kp increase, decrease, or remain the same? Explain.
The way you do this problem is to calculate Q and compare with K. Here is a good site.
http://www.ausetute.com.au/qquotient.html
So basically for the first 3 answers (Part (A)(B)(C)):
(A)and(B) - the concentrations would be equal since the mole ratio is equal and Q = K at equilibrium.
(C) - the rate of both reactions would be equal also, as Q = k, right?
(D)(1) - If the volume is increased at constant temperature their will be a shift to the right, if i am correct, because as the pressure decreases due to the increase in volume the shift will be towards the side which contains the most moles of gas. Thus the number of moles of PCl5 would decrease.
(2) - I am sort of confused for number 2, but I predict the Kp value would increase since the pressure of PCl5 decreases and it is causing the denominator of Kp equation (Kp = Kp(prod)/Kp(react)) to decrease.
So, I was wondering if I am thinking this clearly and if I am on the right path?
for d(2) K would remain the same because k only depends on temperature
(A) To compare the concentrations of PCl3 and Cl2 at equilibrium, we need to examine the balanced equation of the reaction:
PCl5 --> PCl3 + Cl2
From the balanced equation, we can determine the stoichiometric ratio between PCl3 and Cl2. It is clear that one mole of PCl5 produces one mole of PCl3 and one mole of Cl2. Therefore, the ratio of their concentrations at equilibrium will be 1:1.
So, when equilibrium is established, the concentration of PCl3 will be equal to the concentration of Cl2.
(B) Similar to part (A), we can compare the concentrations of PCl5 and PCl3 at equilibrium using the stoichiometric ratio in the balanced equation. From the equation, we can see that one mole of PCl5 produces one mole of PCl3. Therefore, the concentration of PCl5 will be equal to the concentration of PCl3 at equilibrium.
So, when equilibrium is established, the concentration of PCl5 will be equal to the concentration of PCl3.
(C) In a chemical reaction at equilibrium, the rate of the forward reaction is equal to the rate of the reverse reaction. This principle is known as the principle of microscopic reversibility. At equilibrium, the concentrations of reactants and products remain constant because the rates of the forward and reverse reactions are balanced.
Therefore, when equilibrium is established, the rate of the forward reaction will be equal to the rate of the reverse reaction.
(D)
(1) When the volume of the container is increased at constant temperature, it will cause a decrease in the pressure inside the container. According to Le Chatelier's principle, the system will try to counteract the effect of decreasing pressure by shifting the equilibrium position in the direction that produces more moles of gas.
In the given reaction, PCl5 is the only gas present, so increasing the volume will result in a decrease in the number of moles of PCl5. This occurs by shifting the equilibrium towards the reactants (PCl5) to increase the concentration of gas molecules.
Therefore, by increasing the volume, the number of moles of PCl5 in the system will decrease.
(2) The value of Kp, which represents the equilibrium constant, is not affected by changes in temperature, pressure, or volume (as long as the temperature remains constant). The equilibrium constant is determined solely by the stoichiometry of the reaction and the temperature.
So, when the volume of the container is increased at constant temperature, the value of Kp will remain the same. The equilibrium concentrations of PCl3, Cl2, and PCl5 may change, but the ratio of their concentrations remains constant.