Calorimetry
Chapter 5
Calorimetry
Since we cannot
know the exact
enthalpy of the
reactants and
products, we measure
H through
calorimetry, the
measurement of heat
flow.
Calorimetry Functions
• Can be used to determine:
– Heat capacities
– Enthalpies of vaporization (amount of heat
required to change from a liquid to a solid)
– Enthalpies of fusion (amount of heat lost to
change from a liquid to a solid)
– Enthalpies of chemical reactions (how much
heat is gained or lost from a reaction)
Heat Capacity and Specific Heat
• The amount of energy required to raise
the temperature of a substance by 1 K
(1C) is its heat capacity.
• We define specific heat capacity (or
simply specific heat) as the amount of
energy required to raise the temperature
of 1 g of a substance by 1C (1 K).
Heat
q = m*c*ΔT
q= heat
m= mass
c= specific heat
ΔT= final – initial temperature
Heat Capacity and Specific Heat
Specific heat, then, is
Specific heat =
heat transferred
mass  temperature change
q
c=
m  T
Constant Pressure Calorimetry
By carrying out a
reaction in aqueous
solution in a simple
calorimeter such as this
one, one can indirectly
measure the heat
change for the system
by measuring the heat
change for the water in
the calorimeter.
Constant Pressure Calorimetry
Because the specific
heat for water is well
known (4.184 J/mol-K),
we can measure H for
the reaction with this
equation:
q = m  c  T
Calorimetry Concepts
• Heat is always transferred from warmer object to
cooler object
• If two object do not have the same specific heat,
they will not have the same changes in
temperature
• Law of Conservation of Energy applies to heat
transfer.
– Heat lost by object 1 is the amount of heat gained by
object 2.
• Heat is not the same thing as temperature.
Practice Problem
If the temperature of a 34.4 g of ethanol
increases from 25.0°C to 78.8°C, how
much heat has been absorbed by the
ethanol?
Practice Question
If a 50 g unknown metal with a temperature of
115.0°C, is placed in 125 g of 25.6°C water in
a foam cup calorimeter and the metal causes
the water to raise it’s temperature to 29.3°C,
what is the specific heat of the metal?
Part 1: solve the heat the water gained
Part 2: heat gained by water = heat lost by
metal
Part 3: Using the change in temperature of the
metal = final T of water – initial T of metal