# A frictionless piston-cylinder device initially contains air at 150 kPa and 300K. ?Ideal gas qn?

At this stage, the piston is first resting on a set of stop as shown, and the enclosed volume is 0.25 m3. An internal air pressure of 500 kPa is required to move up the piston.The air in the cylinder is now heated until its final temperature is 1500K. Determine work done (in kJ) by the air in the process

### 2 Answers

- NCSLv 72 months ago
Diagram is important in that it gives you the area (diameter, radius) of the piston.

Using the initial conditions, find the "n" in

pV = nRT

150e3Pa * 0.25m³ = n * 8.314J/mol·K * 300K

n = 15.0 mol

"internal air pressure of 500 kPa" tells you that final pressure on the system is 500 kPa (assuming that's the absolute pressure, which it should be).

Calculate the final volume using p, n, R and the final temperature:

500e3Pa * V = 15.0mol * 8.314J/mol·K * 1500K

V = 0.375 m³

work = 500e3Pa * (0.375 - 0.25)m³ = 6.25e4 J = 62.5 kJ