Thermochemistry
Calorimetry
The Measurement of Heat Transfer in Chemical Reactions
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
Heats of Reaction
 Heat
of reaction,
qrxn
– The quantity of heat exchanged between a
system and its surroundings when a chemical
reaction occurs The
within
theproduces
system,energy,
at constant
flame
one
temperature. form of which is heat, q
Heats of Reaction
 Exothermic reactions
– Produce heat, qrxn < 0
q is signed
 Endothermic
reactions
– Absorb heat, qrxn > 0
 Calorimeter
– A device for measuring quantities of heat
produced or absorbed in a chemical reaction
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)
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
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
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, C2H6O
– diesel fuel, C14H30 (similar to kerosene or lamp oil)
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
Simple Combustion Calorimeter
qrxn + qwater = 0
q = mcDT
(used for solutions and water)
q = nDH
(used for reactions)
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?
What Data Should I Collect?

Mass of fuel burned
 Volume (or mass) of water heated
 Temperature change of water
This investigation, Author
3: Introduction and Conclusion
1: Discussion
2: Data/Results and Experimental
This investigation, Author
B: Introduction, Conclusion, Data/Results
A: Discussion and Experimental