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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? 1060 Hixson-Lied Student Success Center 515-294-6624 [email protected] 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