Could you go over #2 & #3 from summer 2009 problem set #11?
Thanks

#2 is an algebra problem.

NO2(g) + 2 H2S(g) <=> NS2(g) + 2 H2O(g)

ΔGrxn = (1)(-ΔGf(NO2(g))) + (2)(-ΔGf(H2S(g))) + (1)(ΔGf(NS2(g))) + (2)(ΔGf(H2O(g)))

From the problem and the tables in your book, you know all of the values in this equation except ΔGf(NS2(g)). Plug in and solve for ΔGf(NS2(g)).

#3 has a couple parts. First, write out a balanced net ionic equation, it will be difficult to handle this problem if you use a full molecular equation. This is just a backwards Ksp process, so the net ionic equation is:

Pb2+(aq) + 2 Cl-(aq) <=> PbCl2(s)

Calculate ΔG for this reaction at standard conditions.

ΔG = ΔGo + RTlnQ

ΔG = ΔGo + RTlnQ

Q = 1 / {[Pb2+][Cl-]2}