Calorimetry

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Calorimetry
Thermochemistry
The Measurement of Heat Transfer in Chemical
Reactions
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Conservation of Energy

• In interactions between a system and its
  surroundings the total energy remains constant
• Energy is neither created nor destroyed

qsystem qsurroundings 0
qsystem -qsurroundings
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Heats of Reaction

• Heat of reaction, qrxn
• 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
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Heats of Reaction

• Exothermic reactions
• Produce heat, qrxn lt 0
• Endothermic reactions
• Absorb heat, qrxn gt 0
• Calorimeter
• A device for measuring quantities of heat
  produced or absorbed in a chemical reaction

q is signed
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Polystyrene Foam Cup Calorimeter

• A simple calorimeter
• Well-insulated nearly isolated
• Measure temperature change of solution inside

qrxn qsoln 0
qrxn is extensive (units are J) DHrxn qrxn/n
is intensive (units are J/mol)
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Polystyrene Foam Cup Calorimeter

• A simple calorimeter
• Well-insulated nearly isolated
• Measure temperature change of solution inside

qrxn qsoln 0
qsoln is extensive (units are J) qsoln
msolncsolnDTsoln
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Polystyrene Foam Cup Calorimeter

• A simple calorimeter
• Well-insulated nearly isolated
• Measure temperature change of solution inside

qrxn qsoln 0
Can be expanded to
nDHrxn msolncsolnDTsoln 0

Energy produced in the reaction
Energy absorbed by the medium
0
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Heat of Combustion of Fuels

• DHcombustion relates to the economy of the fuel
  as an energy source
• Two ways to report
• qcombustion per gram of fuel
• qcombustion per mole of fuel
• This week Determine the amount of energy
  produced (per g and mol) for the combustion of
• ethanol
• diesel fuel, C14H30 (similar to kerosene or lamp
  oil)

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A Simpler Calorimeter

• A soda can and an alcohol burner.
• Not well insulated.
• Measure temperature change.

qrxn qwater ? 0
Can be expanded to
nDHcomb mwatercwaterDTwater ? 0

Energy produced by combustion
Energy absorbed by the water
? 0
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Simple Combustion Calorimeter

• qrxn qwater 0
• q mcDT (used for solutions and water)
• q nDH (used for reactions)

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Notes for Lab This Week

• Total volume should be constant for all runs
• Accurate values for DH 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?

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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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