# Excited gas question

1. Apr 8, 2009

### BurnKero

I have a question in regards to using gas to operate a closed system, To utilize the kinetic energy of the gas molecules to do mechanical work. Conventionally atmoshperic air has been used. The system (air) is pressurized to say 60 lbs and you may get 2 or 3 uses from that pressure. Lets say argon or other heavier gas was used, At the same pressure OF 60 LBS would more mechanical work be done by this gas? I would assume yes since the larger more massive molecule has more energy.

I guess my question can be summarized as. In a pressurized closed system, Would argon be able to do more work than atmospheric air at 60 lbs? Basically the gas is just pushing a piston.

Thank you

2. Apr 9, 2009

### BosonJaw

Well energy must be conserved so I would imagine that the amount of work done to pressurize the system would change proportionally to the energy of the new system.

If your air system has energy X at 60 psi then an argon system may have energy X+10 at 60 psi, However the work done to pressurize the system to 60 pounds would also increase by the arbitrary amount of 10.

Anyway that's just my humble intuition, Help me out guys!!

3. Apr 10, 2009

### Bob S

Suppose we have a cube of 22.4 liters (0.0224 m3) volume, at a standard temperature of T= 273 kelvin and pressure P0=1 atm (~ 100 kPa)) and contains 1 Avagadro's number of molecules, independent of the type of gas. This is a statement of the ideal gas law. The force on each side of the cube is F = A (P-P0) where A = [0.0224 m3]2/3=0.0794 m2 is the area of one side of the cube. The force F on each side of the cube at pressure P > P0 is

F = 0.0794 (P - P0) Newtons

If P - P0 = 400 kPa, then

F = .0794 x 400 kPa = 31,760 Newtons. independent of the type of gas.

The energy required to store the gas in this volume at 60 psi = 400 kPa is independent of the type of gas.