∆S and ∆G Homework
For the first three reactions below, indicate whether you believe the entropy for
the reaction is positive or negative:
1) ____ NaN3(s) à ____ Na3N(s) + ____ N2(g) POSITIVE
2) ____ Al(s) + ____ Br2(l) à ____ AlBr3(s) NEGATIVE
3) ____ Hg(l) + ____ O2(g) à ____ HgO(s) NEGATIVE
Solve the following problems regarding entropy and the spontaneity of chemical
reactions:
4) A chemical reaction has a ∆Hrxn of – 157 kJ and a ∆Srxn of – 221 J/K. Is
this reaction spontaneous at 525 K?
ΔG = -157 -- (525)(-0.221)
ΔG = -40.975
YES, this reaction will be SPONTANEOUS BECAUSE,
+ΔG = non-spontaneous
-ΔG = spontaneous
ΔG = 0 = equilibrium
5) At what temperature is the reaction from problem #4 at equilibrium?
0 = -157 – (T)(-0.221)
157 = -(T)(-0.221)
-157 = T(-0.221)
T = 710 K
6) If a chemical reaction is at equilibrium at 298 K and ∆Srxn = -89 J/K, what
is ∆Hrxn for this process?
ΔH = -26.522
7) What is ∆G for the reaction in problem 6 at 398 K? Is this reaction
spontaneous?
ΔG = 8.9
NO, this reaction is NON-SPONTANEOUS
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