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Chapter 16: Thermodynamics

Chapter 16: Thermodynamics. Kinetics vs. Thermodynamics (speed vs. spontaneity) First Law of Thermodynamics ( Review from Ch. 6 ) D E, q, w, D H, q p , q v Hess’ Law Entropy and the Second Law of Thermodynamics Definition of Entropy - Microstates Spontaneity and D S of the Universe

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Chapter 16: Thermodynamics

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  1. Chapter 16: Thermodynamics • Kinetics vs. Thermodynamics (speed vs. spontaneity) • First Law of Thermodynamics (Review from Ch. 6) • DE, q, w, DH, qp, qv • Hess’ Law • Entropy and the Second Law of Thermodynamics • Definition of Entropy - Microstates • Spontaneity and DS of the Universe • Predicting and Calculating DS • Predicting and Calculating DSsurr • Free Energy, DG • Predicting Spontaneity • DG vs. DG° • Equilibrium • Work

  2. Example 1 Use Hess' Law and standard enthalpies of formation to determine DH° for the following reaction. 4 NH3(g)  +  5 O2(g)  4 NO (g)  +  6 H2O (g) Given:

  3. Example 2 The enthalpy of combustion of methane gas is -891 kJ/mole. Calculate DSsurr for the combustion of 1 mole of methane at 500°C.

  4. Example 3 Which of the following would you expect to be spontaneous at constant T and P? • C12H22O11(s)  12 C(s) + 11 H2O(g); exothermic • N2(g) + 3 H2(g)  2 NH3 (g); DH° = -91.8 kJ • NaCl(s)  Na+(aq) + Cl-(aq); DH° = 3.98 kJ

  5. Example 4 Calculate DS˚, DS˚surr, and DS˚univ for: 2 H2(g) + O2(g) 2 H2O(l) at 25°C.

  6. Example 5 Find DG° at 25°C for: 2 SO2(g) + O2(g) 2 SO3(g) Given:

  7. Example 6 Find DG° at 25°C for: 2 CO (g) + O2(g) 2 CO2(g) Given: 2 CH4(g) + 3 O2(g) 2 CO(g) + 4 H2O(g); DG° = -1088 kJ CH4(g) + 2 O2(g) CO2(g) + 2 H2O(g); DG° = -801 kJ

  8. Example 7 Find DG° at 25°C for: 2 CH3OH(g) + 3 O2(g) 2 CO2(g) + 4 H2O (g) Given:

  9. Example 8 Estimate the temperature at which HgO decomposes to elemental mercury and O2 gas at 1 atm pressure. 2 HgO (s) 2 Hg (l) + O2(g) For this process: DH° = 304.2 kJ DS° = 414.2 J/K

  10. Example 9 How much work can be obtained from the reaction of 10.0 g of hydrogen gas with 10.0 g of oxygen gas to produce liquid water? Assume the reaction occurs under standard conditions and 25˚C. 2 H2(g) + O2(g) 2 H2O (l) For this process, DH° = -571.6 kJ DS° = -326.4 J/K

  11. Example 10 Find DG for the reaction 2 H2S (g) + SO2(g) 3 S (s) + 2 H2O (g) under the following conditions: T = 25°C PH2S = 1.0 x 10-4 atm PSO2 = 1.0 x 10-2 atm PH2O = 3.0 x 10-3 atm Data from Appendix 4: DGf° values in kJ/mole: H2O(g) = -229; S(s) = 0; SO2(g) = -300; H2S(g) = -34

  12. Example 11 Find K for the oxidation of ethanol to acetic acid at 25°C: CH3CH2OH (l) + O2(g) CH3CO2H(l) + 2 H2O(l) DG° can be found from thermodynamic tables of DGf° values. It is -455 kJ/mole.

  13. Example 12 Use the data below to find Ksp for silver sulfide at 25˚C.

  14. Example 13 The equilibrium constant for the reaction: 2Fe3+ (aq) + Hg22+(aq)2Fe2+ (aq) + 2Hg2+(aq) is 9.1x10-6 at 298K. • What is DG° at this temperature? • If standard state concentrations of the reactants and products are mixed, in which direction does the reaction proceed? • Calculate DG when [Fe3+]=0.20M, [Hg22+]=0.010M, [Fe2+]=0.010M, and [Hg2+]=0.025M.

  15. Example 14 Hydrogen gas is an excellent fuel. It combines With oxygen gas to produce water vapor. • Calculate DH°, DS°, and DG° for the combustion of 1 mole of hydrogen gas at 25˚C if PO2=PH2=PH2O=1 atm. • Is the spontaneity of this reaction dependent upon temperature? If so, at what temperatures is it spontaneous?

  16. Example 15 Hemoglobin molecules carry oxygen from the lungs to tissue cells where the oxygen is then released for use in metabolic processes. The molecule can be represented as Hb in its unoxygenated form and as Hb•O2in its oxygenated form. One reason why carbon monoxide is toxic is that it competes with O2 to bind to Hb: Hb•O2 (aq) + CO(g)Hb•CO(aq) + O2(g) • IfDG°≈-14kJ at 37°C (body temp), what is the ratio of [Hb•CO] to [Hb•O2] at 37°C if [O2]=[CO]? • Use LeChatelier’s Principle to suggest how to treat a victim of CO poisoning.

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