Consider the following equilibrium:

Question

NH4Cl(s)--->NH3(g) + HCl(g)

Suppose a vessel containing NH4Cl(s), NH3(g) and HCl(g) is at equilibrium. If the volume of vessel is instantaneously doubled while keeping the temp constant when a new equilibrium is reacted, which of the following statements is correct?

A) the amount of NH3 and HCl double
B) the partial pressure of NH3 and HCl in the vessel remain unchanged
or

C) the total pressure is halved

I am going with B) because I think that the partial pressure will be unchange because of the solid in the equation. Is this correct?

Answer 1

Kp = pNH3*pHCl = some number. Let's just make up a number, say pNH3 = 5 atm; pHCl = 5 atm, Kp = 5*5 = 25.
Now, if we double the volume, we will half the pressure so if we half NH3 pressure and half pressure HCl, that makes Qp = 2.5*2.5 = 6.25 which means the reaction will shift to the right in order to increase Qp at 5 each up to Kp = 25.
So I think B is correct; i.e., each gas was at 5 atm at first, they are back to 5 atm for the new equilibrium so they haven't changed. Is that the only one that is correct? I don't think so.

Answer 2

I read this question wrong and posted it wrong...it should be which is incorrect? If this is the case shouldn't C be the correct one?

Answer 3

Isn't A the incorrect one? I think both B and C are correct. By the way, I goofed in my post; I should have written.....so if we halve NH3 and halve pressure HCl......