Entropy Tutorial
1. Which one of the following reactions would you expect to have the lowest S?
A.CH4(g) + 2O2(g) CO2(g) + 2H2O(g)
B.C2H2(g) + 5/2O2(g) 2CO2(g) + H2O(g)
C.C2H4(g) + O2(g) 2CO2(g) + 2H2O(g)
D.C2H6(g) + 7/2O2(g) 2CO2(g) + 3H2O(g)
Lower s means product must have lower mole compare to reactants
2. Aluminum forms a layer of aluminum oxide when exposed to air which protects the bulk
metal from further corrosion.
4Al(s) + 3O2(g) 2Al2O3(s)
Using the thermodynamic data provided below, calculate S for this reaction.
A.182.3 J/K·mol
B.131.5 J/K·mol
C.–182.3 J/K·mol
D.–626.2 J/K·mol
3. Sulfur can be separated from lead in the mineral galena, PbS(s), by "roasting" the ore in the
presence of oxygen as shown in the following reaction:
2PbS(s) + 3O2(g) 2PbO(s) + 2SO2(g)
Calculate S for this reaction using the thermodynamic data provided below.
A.–410 J/K·mol
B.–161.5 J/K·mol
C.–47.7 J/K·mol
D.21.8 J/K·mol
4. With respect to the system only, a reaction with H < 0 and S > 0 is predicted to be:
A.Spontaneous at all temperatures
B.Spontaneous at high temperatures only
C.Spontaneous at low temperatures only
D.Nonspontaneous at all temperatures
