Density?????

Question

A gas has density of 36056 g/L at STP. What is its density at 647 torr and 72 degrees C? (answer in units of g/L).
i dont know how to approach this...! :(

sorry, i dont use/have yahoo messenger.. =[

Answer 1

Something is wrong in your data. I don't know any gas that has a mass of 36.056 kg per L. Anyway, find a formula for the density, d, from the state equation of the ideal gases:

p*V = n*R*T. But n = m/Mr (where Mr the relative molar mass) and m = d*V, so

p*V = d*V*R*T/Mr (simplify V and solve for d)

d = p*Mr/R*T

Apply this formula twice, for the STP conditions (p1 = 760 torr and T1 = 273 K) and for p2 = 647 torr and T2 = 72 + 273 = 345 K.

d2 = p2*Mr/R*T2 (1)
d1 = p1*Mr/R*T1 (2)

Divide (1) and (2) and you get:

d2/d1 = p2*T1/p1*T2, so

d2 = d1*P2*T1/P1*T2

d2 = d1*647*273/760*345

d2 = 0.674*d1

Replace d1 and you have the answer. That's it!!!

Answer 2

Assume that you have one litre of the gas at STP.
Find V2, the volume of the gas at the new temperature and pressure. (Use the combined gas law P1V1/T1 = P2V2/T2)

Then, calculate the new density by D = m/V2.
(The mass of the gas will stay the same even if its volume changes.)

Good luck !

Answer 3

I would be glad to help you. I teach chemistry.
Messenger me on Yahoo! Messenger. I can explain it. My messenger ID is
fortitudinousskeptic
- Kevin