hey everyone I've a quick chem question its part of my hw and i'm struggling with it.. question below..

Question

if anyone can explain it and answer it for me.. even if its just an explanation as to how to do it that'd be great guys thanx.. 

here's the question:
Liquid helium at 4.2 K has a density of 0.147 g/mL. Suppose that a 2.50-L metal bottle at 90K contains air at 3.0 atm pressure. If we introduce 100.0 mL of liquid helium, seal the bottle, and allow the entire system to warm to room temperature (25oC), what is the pressure inside the bottle (in atmospheres)?

Richard · Accepted Answer

This may be a theoretical problem and not a practical one.  Helium is unique among the elements as to it's behavior at low temperatures and high pressures (see the phase diagrams at the sites below).

At 4.2 K, the sample of Helium would contain 100.0 mL * 0.147 g/mL = 14.7 grams of Helium.  This would be (14.7 g / 4.003 g/mol) = 3.67 moles of Helium.

If PV = nRT, then P = (nRT)/V

where n = 3.67 moles
R = 0.08206 atm.-L/(mol.-K)
T = 25 °C + 273 K
V = 2.50 L

Calculate the pressure (P) from above.  [You should get something between 35 to 36 atmospheres.]  Remember to add the original 3 atmospheres of pressure provided by the air in the container to the pressure provided by the Helium.

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hey everyone I've a quick chem question its part of my hw and i'm struggling with it.. question below..

1 Answer