2.00 mole of an ideal, monatomic gas

[nkk2008]

Ok, so here is my problem:

Suppose 2.00 mole of an ideal, monatomic gas is initially at a pressure of 3.00 atm and a temperature of 350K. It is expanded irreversibly and adiabatically against a constant external pressure of 1.00 atm until the volume has doubled.

A) Calculate delta S for the system, the surroundings, and the universe (i.e. total).
Hint: To find delta S of system, consider breaking up the expansion into two steps. Based on the properties of and relationships for delta S, think of why you can and must do this.

B)If the absolute entropy per mole of the gas before the expansion is 158.2 J/K mol, calculate delta Gibbs free energy for the process.
Hint: You must use the generally defined relationship for delta G.

We do not want the answers, but my friend and I have no idea where to start. IF you could at least tell us what the hint in part A means we could go from there.

Thank you.

 

[Mapes]

The standard thermo equations apply only to systems in equilibrium, so they're of little use against irreversible processes. A neat trick is to split an irreversible process into multiple reversible parts. (For example, we might extract work via a piston, but then dump that energy right back in as heat.) The starting and ending states are the same, but the requirement of reversibility is now fulfilled and the equations are now tractable. Is this enough to get you started?

 

[nkk2008]

But how do I deal with any changes in temperature? Are there any? In class we learned that delta s equaled q/t, where q was equal to delta h for reversible processes

 

[Mapes]

Remember that it's an ideal gas, and apply the ideal gas law if it simplifies things.