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General Chemistry II- Entropy and Formation of Ammonia (Coursework Sample)

Instructions:

1:Choose the member with the higher entropy in each of the following pairs, and justify your choice
(a)1 mol of SO_2 (g) or 1 mol of SO_3 (g)
(b) 1 mol of CO_2 (s) or 1 mol of CO (g)
(c) 3 mol of O_2 (g) or 2 mol of O_3 (g)
(d) 1 mol of KBr(s) or 1 mol of KBr(aq)
(e) seawater at 2 ᵒC or at 23 ᵒC
(f) 1 mol of CF_4 (g) or 1 mol of CCl_4 (g).
2:Predict the sign of ∆S_rxn^ᵒ and calculate its value for the combustion of 1 mol of propane at 25^0 C.
C_3 H_8 (g) + 5O_2 (g) → 3CO_2 (g) + 4H_2 O(l)
3:At 298 K, the formation of ammonia has a negative △S_sys^0; s
N_2 (g) + 3H_2 (g) → 2NH_3 (g)
∆S_sys(rxn)^0 = –197 J/K Calculate ∆S_univ^0, and state whether the reaction occurs spontaneously at this temperature.

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Content:


GENERAL CHEMISTRY II
STUDENT’S NAME:
INSTITUTION AFFLIATED
DATE
Question 1 Answer
Choose the member with the higher entropy in each of the following pairs, and justify your choice [assume constant temperature, except in part (e)]
(a)1 mol of SO2(g) or 1 mol of SO3 (g)
1 mol of SO3 (g). For equal numbers of moles of substances with the same types of atoms in the same physical state, the more atoms in the molecule (chemical complexity) the higher the entropy.
(b) 1 mol of CO2 (s) or 1 mol of CO (g)
1 mol of CO2(g). For a given substance, entropy increases as the phase changes from solid to liquid to gas.
(c) 3 mol of O2 (g) or 2 mol of O3(g)
3 mol of O2 (g). The two samples contain the same number of oxygen atoms but different numbers of molecules. Although each O3 molecule is more complex than each O2 molecule, the greater number of molecules dominates because there are many more microstates possible for 3 mol of particles than for 2.
(d) 1 mol of KBr(s) or 1 mol of KBr(aq)
1 mol of KBr(aq). The two samples have the same number of ions, but their motion is more limited and their energy less dispersed in the solid than in the solution. An ionic substance in solution usually has a higher entropy than the solid.
(e) seawater at 2 ᵒC or at 23 ᵒC
Seawater at 23°C. Entropy increases with rising temperature.
(f) 1 mol of CF4 (g) or 1 mol of CCl4 (g).
1 mol of CCl4 (g). For similar compounds, entropy increases with molar mass (and/or the radius.
Question 2 Answer
Predict the sign of ∆Srxnᵒ and calculate its value for the combustion of 1 mol of propane at 250 C.
C3H8 (g) + 5O2 (g) → 3CO2 (g) + 4H2O(l)
Compound

C3H8 (g)

O2 (g)

CO2 (g)

H2O(l)

Sᵒ (J/K·mol)

269.9

205.0

213.7

69.9

△Srxnᵒ = [(3 mol CO2)(S°of C+ (4 mol H2O)(S° of H2O)]– [(1 mol C3H8 )(S° of C3H8+ (5 mol O2 )(S° of O2 )]
△Srxnᵒ= [(3mol)(213.7J/K·mol) + (4 mol)(69.9J/K·mol)] – [(1mol)(269.9 J/K·mol) + (5 mol)(205.0 J/K·mol)]
△Srxnᵒ=–374 J/K
Question 3 Answer
At 298 K, the formation of ammonia has a negative △Ssys0; s
N2 (g) + 3H2(g) → 2NH3 (g)
∆Ssysrxn0 = –197 J/K Calculate ∆Suniv0, and state whether the reaction occurs spontaneously at this temperature.
Solution
Compound

N2 (g

...
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