Chemistry problem.. need help before exam tomorrow please??

Question

PH3BCl3(s) decomposes at 60°C as follows:

PH3BCl3(s) <-----> PH3(g) + BCl3(g)

Kp = 0.052 for the reaction. Starting with only 3.0 mol of PH3BCl3(s) in a 10.0 L reaction vessel, the reaction is allowed to reach equilibrium. What is the total gas pressure at 60°C?

a. 0.23 atm

b. 0.46 atm

c. 0.052 atm

d. 0.10 atm

B is the right answer, but I need to how to get the answer, I have no idea how to do this problem because there arent any pressures given in the problem, how do you solve for a pressure without being given a pressure???

10 points for best answer!!!

Answer 1

Your starting pressure was one atm, unless otherwise stated...but here the problem probably stated that you started in a vacuum.

Three mols of solid were converted to SIX mols of gas, confined to 10 liter volume at 60*C (333*K).

Plug these values into the Ideal Gas Equation to get the (approx...gases are not ideal) answer.