An empty 5.00-L flask is charged with 0.250 g of pure H2S(g), at 25 C. Q=0, pres

Question

An empty 5.00-L flask is charged with 0.250 g of pure H2S(g), at 25 C. Q=0, pressure of ammonia is zero. Initial pressure of H2S(g) in the flask is 3.59*10^-2 atm. In addition to the H2S already present in the flask, solid NH4HS is added until there is excess unreacted solid remaining.

What are the partial pressures of NH3 and H2S at equilibrium, that is, what are the values of PNH3 and PH2S, respectively?

Enter the partial pressure of ammonia followed by the partial pressure of hydrogen sulfide numerically in atmospheres separated by a comma.

Answer is not: PNH3 = 0.319 atm and PH2S = 0.376 atm
mole fraction H2S = 0.319 atm / 0.695 atm = 0.459

Explanation / Answer

moles of H2S = 0.250/34 = 0.0074

NH4HS(s) = (constant)
NH3 = x
H2S = x

Kp = P[NH3]*P[H2S]/1 = 0.189

substitute equilibrium values from the table

0.189= x^2

x = 0.435 atm =PNH3 = PH2S

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