2009/07/19

Sorry, I had a network problem...

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 from tabulated values. {I don't have a book with tabulated thermodynamic values handy so I can't calculate an exact value for you...} Once you know ΔGo, plug in to calculate under non-standard conditions.

ΔG = ΔGo + RTlnQ

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

Given the numbers in the problem, the correction term {RTlnQ} will probably only be a few kJ/mol. Remember to use kelvin temperatures and be consistent with kJ and J.

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