Can anyone help me with this, please?(adsbygoogle = window.adsbygoogle || []).push({});

1. 1 mol of an ideal gas is compressed slowly and isothermally at 400 K in a piston-cylinder arrangement. Initial pressure = 100 kPa, final pressure 1000 kPa. The system is surrounded by a resevoir at 300 K such that heat exchange can take place between the piston-cylinder arrangement and the resevoir. System is isolated, so no heat exchange with outside world.

Calculate the entropy change of the gas, resevoir and universe if:

i. the piston is frictionless.

I'm stuck trying to do the entropy change for the gas. If I manage to do it, I should be able to do the rest.

I know delta S = INT dQ/T (haven't used tex before)

Also, from the 1st law: delta U = Qin + Won

For an isothermal change, delta U = 0 (as U depends on T only)

=> Qin = -Won

=> Qin = INT P dV

I'm not sure where to go from there, cos I can't put dQ = P dV in the integral above, can I (then substitute P = nRT/V, obviously)?

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Need help with entropy question

**Physics Forums | Science Articles, Homework Help, Discussion**