Ideal gas question on oxygen

1. May 7, 2006

N_L_

A standard cylinder of oxygen used in a hospital has the following characteristics at room temperature (295 K): gauge pressure = 13,800 kPa (2000 psi), volume = 16 L (0.016 m^3). How long will the cylinder last if the flow rate, measured at atmospheric pressure, is constant at 2.4 liters/min?

I tried to find the volume (in liters) at atmospheric pressure. It didn't come out right.

Since nRT is constant do I need to find the number of moles?

Am I taking the wrong approach?

2. May 7, 2006

Hootenanny

Staff Emeritus
Assuming temperature is constant you could use Boyle's law.

~H

3. May 7, 2006

N_L_

Does that work for gauge pressure?

Thank you.

4. May 7, 2006

Hootenanny

Staff Emeritus
You must first convert it to absolute pressure, remember;

$$P_{gauge} = P_{abs} - P_{atm}$$

~H

5. May 7, 2006

LeonhardEuler

Just add atmospheric pressure to the guage pressure to get absolute pressure.

6. May 11, 2006

N_L_

P absolute = P gauge + P atmospheric

= 13,800 kPa + 101 kPa

= 13,901 kPa

PV = k

If I don't need to know k, how to I use the equation?

7. May 11, 2006

Hootenanny

Staff Emeritus
If you know the pV is constant you can make an equality with respect to the intial and final pressures and volumes, thus;

$$p_{i}V_{i} = p_{f}V_{f}$$

~H

8. May 11, 2006

N_L_

Many thanks for all of the help.