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Two solids dissociate as follows:
     A(s)B(g)+C(g) Kp1=x atm2
     D(s)C(g)+E(g) Kp2=y atm2
The total pressure when both the solids dissociate simultaneously is:
(A) x+y atm
(B) 2x+y atm
(C) (x+y) atm
(D) x2+y2 atm

Answer
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Hint :When a solid dissociates into two gases, we can assume that the pressure of both the gases is the same. So, do that and then try and find the total pressure using equilibrium constant using the pressure of gases.

Complete answer:
We are given that two solids dissociate simultaneously to form gases. We will try and find the total pressure of the mixture of gases.
- In the dissociation reaction of A, we can see that two gases B and C are formed. Both of these gases will have the same pressure because they are produced in the same amounts. So, assume that gases B and C have pressure P1 .
- Same way gases C and E are formed from D. Thus, we can say that the pressure of C and E will be the same. We assume that the pressure of C and E is P2.
Now, we can say that total pressure of C = P1+P2
- Now, for reaction (1), we can write its equilibrium constant in terms of pressure as
     KP1=[Product][Reactant]
But we know that the reactant is solid and it does not have any pressure. So, we can write that
     KP1=[PB][PC]
But we already assumed that PB=P1 and PC=P1+P2
So, we can write that
     KP1=(P1)(P1+P2)
But we are given that KP1=x So,
     x=(P1)(P1+P2) ......(1)
For reaction (2), we can also write that
     KP2=y=PcPE
So, we obtain
     y=(P1+P2)(P2) ...(2)
Adding equations (1) and (2), we get
     x+y=(P1+P2)2
Now, total pressure can be given as
     PT=PC+PB+PE
Putting the available values into above equation, we get
     PT=(P1+P2)+P1+P2=2(P1+P2)
But we obtained that x+y=(P1+P2)2 . So, we can put its value in above equation and we will get
     PT=2x+y

Thus, the correct answer of this question is (B).

Note:
Remember that in the expression of equilibrium constant of the reaction, we can either use molar concentration or partial pressures. We cannot use both at the same time. The equilibrium constant is independent of the inert gases present in the mixture.