# Hydrogen gas liquid equation

1. Mar 22, 2005

### chemister

If 277 L of LIQUID hydrogen has a mass of 19.7 kg, what volume will this amount of hydrogen occupy as a GAS at 25 degrees celcius and 1 atm?

Is there some kind of equation that I can use to make this problem easier?

THANKS!

2. Mar 22, 2005

### Cesium

PV = nRT

You'll use this equation for almost every gas problem.

R (ideal-gas constant) = 0.0821 L-atm/mole-K
V = volume (L)
P = pressure (atm)
n = amount (moles)
T = temperature (K)

V = nRT/P

You need to convert the 19.7 kg H2 to moles H2 and the 25 C to Kelvin.

3. Mar 22, 2005

### chemister

Do you have to take into account the hydrogen beginning as a LIQUID and ending as a GAS?

4. Mar 22, 2005

### Cesium

No because when you go from a liquid to a gas, the number of moles of H2 will still stay the same and therefore you can predict the volume.

5. Mar 22, 2005

### chemister

When converting 19.7 Kg to moles would you use H2 (being 2.0158g) or just H (being 1.0079g)?

6. Mar 22, 2005

### Cesium

Good question. Always use the diatomic molecule...so H2.

7. Mar 22, 2005

### chemister

Thanks for your help. So if i have done things right my answer should be close to 2.39 X 10^5 L

8. Mar 22, 2005

### Cesium

Yes I got a similiar answer. By the way, what value are you using for R? 0.0821 or something more precise?

9. Mar 22, 2005

### chemister

For this problem I just used 0.0821, but usually I use 0.082057