Physical Chemistry II Chem 402 Spring Chapter 4 (4, 9, 10, 14, 16, 18,20, 22)

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1 Physical Chemistry II Chem 402 Spring 2011 Chapter 4 (4, 9, 10, 14, 16, 18,20, 22) P4.4) Calculate H or the process NO(g), 1 bar, K NO(g), 1 bar, 550. K assuming that the heat capacities o reactants and products are constant over the temperature interval at their values at K 550. T T H H NO, g,298.15k CP d K K CP CP, m g CP, m 2 g CP, m 2 g J K mol NO, N, O, J K mol 550. T H H NO, g, K d J mol K NO,, K kj mol 91.3 kj mol kj mol [kj mol ] H g P4.9) Calculate the standard enthalpy o ormation o FeS 2 (s) at 300. C rom the ollowing data at K. Assume that the heat capacities are independent o temperature. Substance Fe(s) FeS 2 (s) Fe 2 O 3 (s) S(rhombic) SO 2 (g) (kj mol H 1 ) C P, m / You are also given that or the reaction 2FeS 2 (s) + 11/2O 2 (g) Fe 2 O 3 (s) + 4SO 2 (g), H = 1655 kj mol 1. 2FeS 2 (s) + 11/2O 2 (g) Fe 2 O 3 (s) + 4SO 2 (g) H reaction = 1655 kj mol

2 kj mol H Fe2O 3, s4h SO 2, g kj mol H Fe O, s 4H SO, g 2H Fe S, s H Fe2S 2, s,298 K kj mol = kj mol The enthalpy o ormation at 300. C is given by K H FeS s,573 K H FeS s,298 K C T dt p 298 K Because the heat capacities are assumed to be independent o T, FeS 2,573 K FeS 2, 298 K, FeS 2,, Fe, 2, S, 573 K 298 K H s H s CPm s CPm s CPm s kj mol J K mol K 298 K [kj mol ] P4.10) The data below are a DSC scan o a solution o a T4 lysozyme mutant. From the data determine T m. Determine also the excess heat capacity int trs intrinsic C P and transition C P CP at T = 308 K. Determine also the excess heat capacities at T = 308 K. In your calculations use the extrapolated curves, shown as dotted lines in the DSC scan, where the y axis shows C P.

3 C trs p = 0.83 J K g C p = 1.25 J K g C int p = 0.42 J K g T m = 304 K P4.14) Several reactions and their standard reaction enthalpies at K are given here: H (kj mol 1 ) CaC 2 (s) + 2H 2 O(l) Ca(OH) 2 (s) + C 2 H 2 (g) Ca(s) + 1/2O 2 (g) CaO(s) CaO(s) + H 2 O(l) Ca(OH) 2 (s) 65.2 The standard enthalpies o combustion o graphite and C 2 H 2 (g) are and kj mol 1, respectively. Calculate the standard enthalpy o ormation o CaC 2 (s) at 25 C. H reaction (kj mol ) Ca(OH) 2 (s) + C 2 H 2 (g) CaC 2 (s) + 2H 2 O(l) CaO(s) + H 2 O(l) Ca(OH) 2 (s) CO 2 (g) + H 2 O(l) C 2 H 2 (s) + 5/2O 2 (s) C(s) + 2O 2 (g) 2CO 2 (g) 2 ( ) Ca(s) + 1/2O 2 (g) CaO(s) C(s) + Ca(s) CaC 2 (s) H = 59.8 kj mol

4 P4.16) The total surace area o the earth consisting o orest, cultivated land, grass land, and desert is 1.49x10 8 km 2. Every year, the mass o carbon ixed by photosynthesis by vegetation covering this land surace according to the reaction g l s g 6CO 6H O C H O 6O is about 450. metric Tons km -2. Calculate the annual enthalpy change resulting rom photosynthetic carbon ixation over the land surace per mole o carbon given the data above. Assume P = 1 bar and T = 298 K. H = H (C 6 H 12 O 6 (s)) 6 H (H 2 O(l)) 6 H (CO 2 (g)) kj mol kj mol kj mol kj mol The number o moles o ixed carbon is: n kg km year 5-2 mc, ixed 7-2 C, ixed mol km year -3 M C kg mol We calculate the enthalpy change per mole o C using the above result: mol km -2 year 2802 kj mol km 2 H H kj year P4.18) A sample o Na 2 SO 4 (s) is dissolved in 225 g o water at 298 K such that the solution is molar in Na 2 SO 4. A temperature rise o C is observed. The calorimeter constant is 330. J K 1. Calculate the enthalpy o solution o Na 2 SO 4 in water at this concentration. Assume that the solution volume is the same as the solvent volume. Compare your result with that calculated using the data in Table 4.1 (Appendix B, Data Tables).

5 m m s 0 H C T C T M H s solution, m HO 2 solution, m H2O, m calorimeter MH2O 225 g g mol J mol 3 o o 75.3 J K mol C 330 J K K mol L kg kg L H s 2 olution, m 2Hsolution, m Na, aq Hsolution, m SO 4, aqh Na2SO 4, s J mol J mol J mol J mol The relative error is 2.52 kj mol 2.4 kj mol 2.52 kj mol 4.8% P4.20) I g o ethanol, C 2 H 5 OH(l) is burned completely in a bomb calorimeter at K, the heat produced is kj. a) Calculate H combustion or ethanol at K. b) Calculate H o ethanol at K. The reaction is C 2 H 5 OH(l) + 3O 2 (g) 3H 2 O(l) + 2CO 2 (g) 2 CO 2, 3 H2O, C2H5OH, CHOH, 2 CO, 3 HO, H H g H l H l H l H H g H l Energy J 1 U 1362 kj mol 1 methanol Methanol g g mol H U nt 1362 kj mol 298 K= 1365 kj mol 1 1 CHOH, 2 CO, 3 HO, H l H H g H l kj mol kj mol kj mol [kj mol ]

6 P4.22) A g sample o sucrose, C 12 H 22 O 11, is burned in a bomb calorimeter at 298 K. In order to produce the same temperature rise in the calorimeter as the reaction, J must be expended. a) Calculate U and H or the combustion o 1 mole o sucrose. b) Using the data tables and your answer to a), calculate H or sucrose. c) The rise in temperature o the calorimeter and its contents as a result o the reaction is K. Calculate the heat capacity o the calorimeter and its contents. The reaction is C 12 H 22 O 11 (s) + 35/2O 2 (g) 11H 2 O(l) + 12CO 2 (g) 12 CO 2, 11 H2O, C12H22O 11, C H O, 12 CO, 11 H O, H H g H l H s H s H H g H l Energy J 3 1 U kj mol 1 msucrose Msucrose g g mol H U nt 5635 kj mol K= kj mol C H O, 12 CO, 11 H O, H l H H g H l kj mol kj mol kj mol kj mol kj mol c) Energy J T K 3 1 Calorimeter constant = [J K ]