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^{3}is filled with gas F

_{2}at a pressure of 250mmHg and a temp of -85 C. a small amount of solid P

_{4}is put into the container and a reaction occurs according to

P

_{4(s)}+ 6F

_{2(g)}--> 4PF

_{3(g)}

the container is again cooled to -85 C and the pressure is now measured at 203mmHg. find the mass of the PF

_{3}

V=0.061 L

T=188.15 K

P

_{i}=0.329atm

P

_{f}=0.267atm

now i don't know if all of the F reacted since i don't know how many mols of P there were so i can't just find the mols of F and multiply. but the most i could have is 2/3 the amount of mols of F

_{2}

using PV=nRT i can say that sincs , V,R,T=const

RT/V=P/n=const

now to find the amount of mols at the beginning, n=PV/RT=1.3*10

^{-3}mol F

_{2}

(P/n)

_{i}=(P/n)

_{f}and i know everything except for n (PF

_{3}) which i calculate to come to 1.055*10

^{-3}mol

from here i can work out the mass of the PF

_{3}

m=n*mw=1.055*10

^{-3}mol*(30.97+3*19)g/mol=

**0.093g**

but if i look at the amount of mols that i have here, something doesn't add up since i was meant to have 2/3 the amount of mols of F

_{2}but i have about 0.8 times the amount of mols of F

_{2}, meaning that i have more mols than i should according to the equation.

what is wrong here?