Samples: Multiple-Choice Questions
- Given the following standard molar entropies measured at 25°C and 1 atm pressure,
calculate ∆S°in (J/K) for the reaction
2 Al(s) + 3 MgO(s) →3 Mg(s) + Al 2 O 3 (s)Al(s) = 28.0 J/K
MgO(s) = 27.0 J/K
Mg(s) = 33.0 J/K
Al 2 O 3 (s)= 51.0 J/KA. −29.0 J/K
B. −13.0 J/K
C. 13.0 J/K
D. 69.0 J/K
E. 139 J/KAnswer: C
∆S°= Σ∆S°products−Σ∆S°reactants
∆S°= [3(33.0) + 51.0] −[2(28.0) + 3(27.0)] = 13.0 J/K- For the given reaction and the following information, calculate ∆G°at 25°C.
2 PbO(s) + 2 SO 2 (g) →2 PbS(s) + 3 O 2 (g)Species ∆H°(kJ/mole) ∆S°(J/mole ⋅K)
at 25°C and 1 atm at 25°C and 1 atm
PbO(s) −218.0 70.0
SO 2 (g) −297.0 248.0
PbS(s) −100.0 91.0
O 2 (g) — 205.0A. 273.0 kJ
B. 438.0 kJ
C. 634.0 kJ
D. 782.0 kJ
E. 830.0 kJEnergy and Spontaneity