# Homework Help: Thermodynamics/Ideal gas

1. Jul 13, 2007

### glitchy

Hey all,
got a few questions i need help at. any hlep is fully appreciated.

A rigid sealed 50-liter tank contains argon at a pressure of 5MPa and 400K.
1. What is the mass of argon - what i did here was use PV=mRT, so that means (5000kPa)(50)=m(value from table)(400). what i'm slightly confused about is the Volume, is it correct to us 50?

2. The contents of the tank are then heated so that pressure is doubled, wht is the resulting temp? - wont i us the same formula but just double the pressure and use the value of 'm' that i got from the first part.

Thank you.

2. Jul 13, 2007

### CompuChip

1. Mind the units. Check the table you used to find R. If it has units, for example, m3 Pa / (K mol), you should obviously take the volume in m3, which is not the same a liters (how do you convert them?)

2. Wasn't there something about some equation with p and V being constant?

3. Jul 13, 2007

### Andrew Mason

You just have to get the units right. Using MKS, you must have units of volume in m^3. Pressure is in Pa or N/m^2 and T is in Kelvins. One litre is 10^-3 m^3. and one kPa is 1000 N/m^2.

Use PV = nRT to get the number of moles and use the molar weight of Argon to get the mass.

You don't need m. Since volume remains unchanged, doubling the pressure does what to the temperature?

AM