Equilibrium question?

Question

Ammonium hydrogen sulfide is a crystalline solid that decomposes as follows:
NH4HS (s) --> NH3 (g) + H2S (g)

Some solid NH4HS is placed in an evacuated vessel at 25 degrees C. After equilibrium is attained, the total pressure insde the vessel is found to be 0.659 atmosphere. Some solid NH4HS remains in the vessel at equilibrium. For this decomposition, write the expression for Kp and calculate its numerical value at 25 degrees C.

my AP Chem homework...
yeahh... thanks to anyone who helps

Thanks cattbarf... but what do you do with the temperature, and the solid left over?
Also, does this equation have anything to do with the problem?

Kp = Kc (RT) ^ delta ng

-thanks-

Answer 1

Since the vessel is evacuated, initially the pressure inside the vessel is zero atm.
The final pressure (0.659 atm) is due to the decomposition products of gaseous NH3 and H2S. Since the partial pressures of gases are directly proportional to their number of moles,
P(NH3) = 0.659 / 2 = 0.3295 atm
P(H2S) = 0.659 / 2 = 0.3295 atm
(since the moles of both gases are the same)

Kp = P(NH3) x P(H2S)
Kp = (0.3295 atm) x (0.3295 atm)
Kp = 0.11 atm^2

Answer 2

When you post a reply to someone, they probably won't see it. They have answered the question and moved on. They have no reason to go back to the question. Instead, you should send them an email, repeat the entire question and answer, or provide a link to the question in your email.

btw: 25 degrees was the temp at which the data was obtained and therefore is the temp at which Kp will be valid.

Answer 3

Your equilibrium equation is
[NH3][H2S]= Kp, since if you have solid the "activity" of the solid in the gaseous phase is 1. Since equal moles of each has been formed, the partial pressure of each is 0.33 atm. So your answer is [0.33]^2 or 0.109 atm^2.

Answer 4

OMG! What language was that??