[Anthasci]

I've frantically tried to solve this problem, but I just feel like there's something missing ... Here it is:

A reaction container with V=100dm³ is filled with H₂(g) and P₂(g) at T=800K. The starting partial pressures of both components are equal to 1 bar. Once the reaction:

3H₂(g) + P₂(g)  2PH₃(g)

reaches equilibrium, the total pressure inside the container is 1,9 bar. Calculate the equilibrium constant K for the reaction at 800K.

[K=0.012]

I started by calculating the total amount of moles of reactants (I assumed the container is fully filled) and given that pressure is 2 bar, I came with the result n_tot = 0,33256 mol
But when I wanted to calculate the molar fractions, I found out I'm missing information about pressure of a pure component
p_i = x_i · p*_i would then ideally give me the molar fractions and I'd be left with only one variable, β for example (where 2β is the amount of generated phosphane and 3β and β are the amounts of hydrogen and phosphorous, respectively, that reacted. I'm pretty sure I'm on the right way here, but overlooking some detail. Anyone care to point me in the right direction?

Thanks

[Borek]

Why do you start with sum of initial amounts instead of calculating individual initial amounts?

[curiouscat]

By PV=nRT how many total moles left at end?

Also how many mols of each component at start?

[Anthasci]

Oh, I get it now ... the moles of both starting components are the same and the mixture at the end contains 0,35 moles of gas. This should give me the required information to calculate the K.

I also provided the wrong equation, it should be p_i = x_i · p because I was calculating (or trying to) the fractions in a liquid and forgetting that I already have two gaseous phases. Thanks to both It's amazing how late hours can distort your thinking process