a container with a volume of 61cm(adsbygoogle = window.adsbygoogle || []).push({}); ^{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 dont know if all of the F reacted since i dont know how many mols of P there were so i cant 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 doesnt 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?

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# Homework Help: Chemistry- ideal gases

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