A balloon filled with 40 moles of He at 3 atm pressure and at room temperature (300 K) expands isothermally from a volume Vi to a volume Vf till its pressure falls to 1 atm.

(a) What are Vi and Vf?

Here's what I did for this one:

PV = nRT

Vi = nRT/P = (40)(8.315)(300K)/[3*(1.013 x 105 N/m2) = 0.33 m3

Vf = nRT/P = (40)(8.315)(300K)/(1.013 x 105 N/m2) = 0.98 m3

Does this look correct to you?

(b) What is the work done during the expansion?

Here's what I did for this one:

W = nRT ln Vi/Vf = (40)(8.315)(300) ln 0.33/0.98 = 108606.5 J

Does this look correct?

(c) What is ΔU?

I know ΔU = W - Q. If part (b) is correct, I know that W = 108606.5 J, but what is Q? How do I calculate Q?

(d) What is Q (heat exchanged) during the process?

This is just a reiteration of my own previous question, as without Q, I don't know how to calculate ΔU.

(e) Calculate ΔS directly from the Sackur-Tetrode equation.

I am uncertain as to what variables go with what, and still cannot do this since I don't know Q.