Kc = 1.87 10-3 for the following reaction.

PH3BCl3(s)=>PH3(g) + BCl3(g)
(a) Calculate the equilibrium concentrations of PH3 and BCl3 if a solid sample of PH3BCl3 is placed in a closed vessel and decomposes until equilibrium is reached.
(b) If the flask has a volume of 0.400 L, what is the minimum mass of PH3BCl3(s) that must be added to the flask in order to achieve equilibrium?

I got part a (0.0432 M) but I can't get part b, please help!

2 answers

Never mind! I got the answer, I was using 115.69 g/mol rather than 151.09 g/mol for PH3BCl3 (I calculated it for 2 Cl atoms rather than 3)
How did you get part B?!