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Calorimetry
Thermochemistry
Calorimeter
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Instrument used to measure
amount of energy involved in a
chemical reaction.
It is equivalent to an isolated or
closed system. (nothing may enter
or exit the system)
The energy change is not measured
within the system, but the energy
transferred to its surroundings.
A basic calorimeter
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Two Styrofoam cups nestled within
one another (insulation), then filled
with a specific quantity of water
and covered with another cup as a
cover.
A chemical reaction or phase
change takes place inside and a
thermometer is placed within to
measure any change in temperature
that occurs to the system.
Assumptions
1.
2.
3.
It is an isolated or closed system
and there is no heat transfer
between the calorimeter and its
surroundings.
The amount of heat absorbed or
released by the calorimeter itself
is too small to influence
calculations.
Any dilute solutions involved in the
reaction are treated as if they are
water.
Bomb calorimeter
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Cannot use basic design for
combustion reactions.
Used in research for H for fuels,
oils, food, explosives…
Larger and more sophisticated
The reaction container is strong
enough to with stand an explosion,
hence the name “bomb”
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Have fixed components, like volume of
water, thermometer…
Heavily insulated or vacuum insulated so
no convection or conduction can occur
affecting the enthalpy of the system.
Often use the equation: q=CΔT
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Ccalorimetre:
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Ctotal = Cwater + Cthermometre +Cstirrer + Ccontainer
A Bomb Calorimeter
The main idea:
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qsystem =-qsurroundings
System = reaction
Surroundings = calorimeter (water)
Solving calorimeter questions:
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For a regular calorimeter (not bomb):
 Heat released by the reaction = heat absorbed by the
calorimeter + heat absorbed by water in the
calorimeter
 q = mcΔT(calorimeter) + mcΔT(water)
Note: When a styrene (Styrofoam) cup is used, often it is
ignored in the calculations. It is assumed that the heat
absorbed by the cup is negligible. If the heat absorbed by
the cup should be included in the calculations, information
about the heat capacity or specific heat capacity will be
given in the question.
Example:
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A 92.0g sample of a substance with a temperature
of 55ºC is placed in a large scale polystyrene
calorimeter. It contains 1.00 kg of water at
20.0ºC. The final temperature of the system is
25.2ºC.
a) How much heat did the substance release?
b) What is the specific heat capacity of the
substance?
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You can assume the amount of energy
absorbed by the polystyrene is negligible.
So…calculate heat gained by water
q = mcΔT
= (1000g)(4.18)(25.2-20)
= 21736 J (absorbed by water)
a) Therefore substance lost (-) 21736J
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b)
q = mcΔT
-21736 = (92)c(25.2-55)
-21736 = c
-2741
7.9 J/g ·ºC = c
Problems
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Pg 664 #1  4
WS: Calorimetry