110119 - Calorimetry (Chapter 3 p. 59-74) measuring heat,...

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1 CHM3400 - Lecture 6 Jan 19 Calorimetry (Chapter 3 p. 59-74) • measuring heat, heat capacities • bomb calorimetry • differential scanning calorimetry (appl. protein folding energetics) • standard enthalpy of formation and reaction • bond enthalpies
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2 Bomb calorimeter Combustion of sample heats up bomb, which again heats up the water. Monitor T for the water. Note that the bomb and water are in thermal contact, whereas the outside environment (the lab) is thermally isolated from the system. Is this a constant pressure or constant volume expt? ... = + = + = V P q w q U v v
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3 Example 3.6 When a 0.5122 g sample of naphthalene (C 10 H 8 ) was burned in a constant- volume bomb calorimeter, the temperature of the water in the inner jacket rose from 20.17 o C to 24.08 o C. If the effective heat capacity (C V ) of the bomb calorimeter is 5267.9 JK -1 , calculate U and H for the combustion of naphthalene in kJ mol -1 . C 10 H 8 (s) + 12 O 2 (g) → 10 CO 2 (g) + 4 H 2 O(l) Typically excess of O 2 (30 atm) Reaction : Amount of heat generated : C V T = 5267.8 (JK -1 ) x 3.91 (K) = 20.60 kJ U for naphthalene combustion (kJ mol -1 ): 1 .... ) ( 5122 . 0 ) ( 60 . 20 = = = kJmol g kJ U q v How do we calculate H? Why negative?
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4 Enthalpy of combustion in bomb calorimetry C 10 H 8 (s) + 12 O 2 (g) → 10 CO 2 (g) + 4 H 2 O(l) Reaction : gas Change in the number of moles of gas. H =
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This note was uploaded on 05/29/2011 for the course CHM 3400 taught by Professor Seabra during the Spring '08 term at University of Florida.

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110119 - Calorimetry (Chapter 3 p. 59-74) measuring heat,...

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