1. Ifδh= -120.0 Kjandδs= -0.300Kj/K, the Reaction Is Spontaneous Below a Certain Temperature

Leader: Lillian Howard Intro To Gibbs Free Energy Course: Chem 178 (B) Supplemental Instruction Instructor: Dr. Burnett Iowa State University Date: 4/10/13

1. If ΔH = -120.0 kJ and ΔS = -0.300 kJ/K, the reaction is spontaneous below a certain temperature. Calculate that temperature.

2. a. Calculate ΔH and ΔS for the following reaction. b. Is this reaction Endothermic or Exothermic c. Determine the ΔG˚ for this reaction at 25˚C d. Illustrate why NH4NO3 spontaneously dissolves is water at room temperature

+ - NH4NO3(s) + H2O(l)  NH4 (aq) + NO3 (aq)

o o Compound Hf (kJ/mol) S (J/mol-K)

NH4NO3 (s) -365.56 151.08 + NH4 (aq) -132.51 113.40 - NO3 (aq) -205.0 146.40

3. For the Oxidation of Iron to Rust 4Fe + 3O2  2Fe2O3

ΔH˚ rxn -1648.4 kJ/mol

ΔS˚ rxn -543.7 J/(mol K)

What is the standard Gibbs free energy (ΔG˚ rxn ) for this reaction?

1060 Hixson-Lied Student Success Center v 515-294-6624 v [email protected] v http://www.si.iastate.edu 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