1. The Measurement of Heat Transfer in Chemical Reactions
Thermochemistry
Calorimetry
The Measurement of Heat Transfer in Chemical Reactions
Thermochemistry branch of chemistry concerned with heat effects accompanying chemical reactions.
Direct and indirect measurement of heat.
Answer practical questions: why is natural gas a better fuel than coal, and why do fats have higher energy value than carbohydrates and protiens.

2. 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

3. 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
In practice, the temperature is allowed to change and the heat that is lost or needed as the system returns to its original temperature is calculated.

4. q is signed Heats of Reaction Exothermic reactions
Produce heat, qrxn < 0
Endothermic reactions
Absorb heat, qrxn > 0
Calorimeter
A device for measuring quantities of heat produced or absorbed in a chemical reaction
q is signed
Heat of reaction in an isolated system produces a change in the thermal energy of the system. The causes a temperature change.
In an non-isolated system the temperature remains constant and the heat is transferred to the surroundings.
Top picture is CaO(s) + H2O(l) → Ca(OH)2
Bottome picture is Ba(OH)2·8H2O + 2NH4Cl(s)→BaCl2(s) + 2 NH3(aq) + 8 H2O(l)

5. 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)

6. 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

7. 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

8. 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)

9. 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

10. Simple Combustion Calorimeter
qrxn + qwater = 0
q = mcDT (used for solutions and water)
q = nDH (used for reactions)

11. 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?

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
A: Introduction, Conclusion, Data/Results
B: Discussion and Experimental