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Calorimetry Thermochemistry The Measurement of Heat Transfer in Chemical Reactions.

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Presentation on theme: "Calorimetry Thermochemistry The Measurement of Heat Transfer in Chemical Reactions."— Presentation transcript:

1 Calorimetry Thermochemistry The Measurement of Heat Transfer in Chemical Reactions

2 Conservation of Energy In interactions between a system and its surroundings the total energy remains constant: Energy is neither created nor destroyed q system + q surroundings = 0 q system = -q surroundings

3 Heats of Reaction  Heat of reaction, q rxn –The quantity of heat exchanged between a system and its surroundings when a chemical reaction occurs within the system, at constant temperature. The flame produces energy, one form of which is heat, q

4 Heats of Reaction  Exothermic reactions –Produce heat, q rxn < 0  Endothermic reactions –Absorb heat, q rxn > 0  Calorimeter –A device for measuring quantities of heat produced or absorbed in a chemical reaction q is signed

5 Polystyrene Foam Cup Calorimeter  A simple calorimeter –Well-insulated; nearly isolated –Measure temperature change of solution inside q rxn + q soln = 0 q rxn is extensive (units are J)  H rxn = q rxn /n is intensive (units are J/mol)

6 Polystyrene Foam Cup Calorimeter  A simple calorimeter –Well-insulated; nearly isolated –Measure temperature change of solution inside q rxn + q soln = 0 q soln is extensive (units are J) q soln = m soln c soln  T soln

7 Polystyrene Foam Cup Calorimeter  A simple calorimeter –Well-insulated; nearly isolated –Measure temperature change of solution inside q rxn + q soln = 0 Can be expanded to… Energy produced in the reaction Energy absorbed by the medium + = 0 n  H rxn + m soln c soln  T soln = 0

8 Heat of Combustion of Fuels   H combustion relates to the economy of the fuel as an energy source  Two ways to report: –q combustion per gram of fuel –q combustion per mole of fuel  This week: Determine the amount of energy produced (per g and mol) for the combustion of –ethanol –diesel fuel, C 14 H 30 (similar to kerosene or lamp oil)

9 A Simpler Calorimeter  A soda can and an “alcohol” burner. –Not well insulated. –Measure temperature change. q rxn + q water  0 Can be expanded to… Energy produced by combustion Energy absorbed by the water +  0 n  H comb + m water c water  T water  0

10 Simple Combustion Calorimeter q rxn + q water = 0 q = mc  T(used for solutions and water) q = n  H(used for reactions)

11 Notes for Lab This Week  Total volume should be constant for all runs  Accurate values for  H will not be determined… …but relative values between two fuels will be  How will you know how many moles of fuel were burned?  How will you determine the quantity of heat absorbed by the water in the aluminum can calorimeter?

12 What Data Should I Collect?  Mass of fuel burned  Volume (or mass) of water heated  Temperature change of water This investigation, Author 1: Introduction and Conclusion 2: Discussion 3: Data/Results and Experimental This investigation, Author A: Introduction, Conclusion, Data/Results B: Discussion and Experimental

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