# The original mass of a gas in a leaky cylinder

1. Dec 1, 2013

### SamQP

1. The problem statement, all variables and given/known data
A leaky cylinder, at 0oC contains gas with a pressure of 18.0 atmospheres.
After being kept at 20oC for 24 hours, the pressure is now 16.3 atmospheres and the masss has fallen by 1.2kg.
What was the gas' original mass?

2. Relevant equations

3. The attempt at a solution
My only thought on how to tackle this is far to simple and ignores important factors like the temperature.
All I could think of doing was diving 1.2 by 1.7 to get the mass per atmosphere and then multiply that by 18, however I know this will not be right.

Any help appreciated.

2. Dec 1, 2013

### Staff: Mentor

You know the initial pressure and temperature, but you don't know the volume of the cylinder or the initial number of moles. Call the volume V and the number of moles n0. What is the relationship between the volume and the initial number of moles?

You said that 1.2 kg of gas leave the cylinder. Do you happen to know that molar mass of the gas? If so, then you know the number of moles that exited (Δn), and the new number of moles (n0-Δn). You also know that the new temperature is 20 C and the new pressure is 16.3 atm. How are the new temperature, the new pressure, and the new number of moles related in terms of n0 and V?