Download 4/10/13 - Iowa State University

Intro To Gibbs Free Energy
Supplemental Instruction
Iowa State University
1.
Leader:
Course:
Instructor:
Date:
Lillian Howard
Chem 178 (B)
Dr. Burnett
4/10/13
If ΔH = -120.0 kJ and ΔS = -0.300 kJ/K, the reaction is spontaneous below a certain
temperature. Calculate that temperature.
2.
a.
b.
c.
d.
Calculate ΔH and ΔS for the following reaction.
Is this reaction Endothermic or Exothermic
Determine the ΔG˚ for this reaction at 25˚C
Illustrate why NH4NO3 spontaneously dissolves is water at room temperature
NH4NO3(s) + H2O(l)  NH4+ (aq) + NO3- (aq)
Compound
NH4NO3 (s)
NH4+ (aq)
NO3- (aq)
3.
For the Oxidation of Iron to Rust
ΔH˚ rxn
ΔS˚ rxn
Hfo(kJ/mol)
-365.56
-132.51
-205.0
So(J/mol-K)
151.08
113.40
146.40
4Fe + 3O2  2Fe2O3
-1648.4 kJ/mol
-543.7 J/(mol K)
What is the standard Gibbs free energy (ΔG˚ rxn ) for this reaction?
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4.
For a certain chemical reaction ΔH˚ = -35.4 kJ and ΔS˚ = - 85.5 J/K.
a. Is this reaction endothermic or exothermic?
b. Does this reaction lead to an increase or decrease in randomness of the system?
c. Calculate ΔG˚ for the reaction at 298 K.
d. Is this reaction spontaneous at 298 K under standard conditions?
5.
For each of the following pairs choose the substance with the higher entropy
a. Ar (l) or Ar (g)
b. He (g) at 3 atm or He (g) at 1.5 atm
c. 1 mol of Ne (g) in 15 L or 1 mol Ne (g) in 1.5 L
d. 1 mol P4 (g) at 300˚ C & 0.01 atm or 1 mol As4 (g) at 300˚ C & 0.01 atm
6.
For the decomposition of barium carbonate, consider the following thermodynamic data:
Calculate the temperature in kelvin above which this reaction is spontaneous.
7.
ΔH ˚
ΔS ˚
ΔG ˚
_____
_____
______
Always spontaneous
_____
_____
______
Always non-spontaneous
_____
_____
______
Spontaneous over a certain temperature
_____
_____
______
Non-spontaneous over a certain temperature