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lect_19nov12f08

# lect_19nov12f08 - Outline 19 12-OCT-2008 1 Review...

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1 Outline 19 12-OCT-2008 1. Review- Calorimetry ΔH rxn = q P , q = C ∆T, (q rxn +q cal =0) 2. Calorimetry- continued ΔE rxn = q V 3. Stoichiometry- heat & moles 1. Thermochemical Eqns Manipulations

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2 q rxn & Calorimetry (Review) Calorimeter - device used to measure heat transferred during physical or chemical change. (next slide) Heat absorbed by calorimeter and its contents is negative of heat of reaction. (because whole apparatus is insulated from rest of surroundings.) rxn r calorimete q q - = Or q cal + q rxn =0 (Calorimeter Equation)
3 Figure 6.11: Coffee-cup calorimeter. Used in Experiment 7

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4 Calorimetry; Ex: 1 Follow-up problem 6.4, p. 248. Given: 10.25 carat diamond (0.2000g/carat) heated to 74.21 ˚C and immersed in 26.05 g water at 27.20 ˚C in constant pressure calorimeter. (c diamond =0.519 J/g*K, c water = 4.184 J/g*K)) Find: Final temperature. Soln: use q = m*c*ΔT & q diamond + q water = 0 (Calorimeter eqn.) & ( At end will have same temp.) Chalk or camera.
5 Calorimetry; Ex. 2 Ex: When 23.6 grams of calcium chloride, CaCl 2 , dissolved in water in calorimeter, temperature rose from 25.0 o C to 38.7 o C. If heat capacity of solution and calorimeter is 1258 J/ o C, what is enthalpy change per mole of calcium chloride? Rxn (process) is H 2 O CaCl 2 (s) CaCl 2 (aq)

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6 Calorimetry; Ex. 2 (cont.1) First, calculate heat absorbed by calorimeter. ) C 0 . 25 C 7 . 38 ( ) 1258 ( T C q o o C J cal o - × = = J 10 72 . 1 q 4 cal × = Have heat, now need moles of calcium chloride. Calcium chloride has molar mass 111.1 g/mol, so # mol CaCl 2 = 23.6 g CaCl 2 *(1 mol CaCl 2 /111.1 g CaCl 2 ) = 0.212 mol CaCl 2
7 Calorimetry; Ex. 2 (Cont.2) mol / kJ 1 . 81 mol 212 . 0

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lect_19nov12f08 - Outline 19 12-OCT-2008 1 Review...

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