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Hess Law

# Hess Law - Hess Law By Robert Pelini Date of Lab Date...

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Hess Law By: Robert Pelini Date of Lab: 3/27/08 Date Submitted: 4/3/08 Partners: Paul Kwasowski

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Calculations: Part 1 : 50mL of 1.0 M HCL ∆T = Tf-Ti 27.47˚C- 19.83˚C = 7.64˚C Specific Heat and Density of .5 M NaCl are 0.96 cal/g˚C and 1.02 g/mL Heat gained by Calorimeter: 4.0 cal/˚C x 7.64˚C = 30.555 cal-> 30 cal Heat gained by the solution: 102 g x .96 cal/g ˚C x 7.64˚C = 740 cal -> 7.4 x 10^2 cal Total heat released by rxn: 30 cal + 740 cal = 677 cal -> 770 cal -> 7.7 x 10^2 cal Heat of rxn: 740 cal / .05 moles NaOH = -1.5 x 10^4 cal/ mol Part 2 : mass of the pellets = 4.0841 ∆T = Tf-Ti 30.70˚C – 21.81˚C = 9.89˚C Heat gained by the Calorimeter: 4.0 cal/˚C x 9.89˚C = 39.56 cal -> 39 cal Heat gained by the solution: 100.0g + 4.0841g = 104.0841g 104.0841g x .94 cal/g˚C x 9.89˚C = 966.8 cal -> 9.668 x 10^2 cal Total heat released by rxn: 966.8 cal + 39 cal = 9.9 x 10^2 cal Heat of the rxn:
Mm of NaOH = 39.996 966.8 cal/( 4.0841g/39.996g/mol) = 8296.89 cal/mol -> -9.8 x 10^3 cal/mol Part 3 : mass of the pellets = 2.0256g ∆T = Tf-Ti 32.79˚C – 20.36˚C = 12.43˚C Heat gained by Calorimeter: 4.0 cal/˚C x 12.43 ˚C = 49.692 cal -> 49 cal Heat gained by solution: (45g + (55mL x 1.20g/mL) + 2.0256g x .96cal/g˚Cx 12.43 = 1216.77 cal -> 1.2 x 10^3 cal Total heat released by rxn: 44 cal + 1200 cal = 1266 cal -> 1.2 x 10^3 cal

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