Constant Pressure Calorimetry (6.3.1)

Question 1

• Heat is measured through a process called calorimetry.

Answer 1

• Heat is measured through a process called calorimetry.

Question 2

• Constant pressure calorimetry is useful for finding heat capacities or for
determining the enthalpy change of reactions.

Answer 2

• Constant pressure calorimetry is useful for finding heat capacities or for
determining the enthalpy change of reactions.

Question 3

Heat is measured through a process called
calorimetry.
Calorimetry relies on the fact that the heat lost by
the system flows into the surroundings.
Therefore, the magnitude of the energy change is
the same for the system and the surroundings, but
the sign of the heat flow is opposite. This is
expressed mathematically as qsys = –qsurr.
Calorimetry can be performed at constant pressure
or at constant volume.
Constant pressure calorimetry involves a simple
experimental setup where the temperature change
of a known amount of water is measured. A
constant pressure calorimeter is not airtight, and
is therefore open to atmospheric pressure, which is
essentially constant.
The heat evolved by a system at constant pressure
is equal to the enthalpy change of that system.
Therefore, constant pressure calorimetry can be
used to determine the enthalpy change of reactions.
Constant pressure calorimetry is also useful for
finding heat capacities. In this example, a known
mass of aluminum was heated to a known
temperature, and then placed in a constant pressure
calorimeter. The change in temperature of the
water (surroundings) was used to calculate the
molar heat capacity of the aluminum.
In this experiment, the moles of water (nH2O), molar
heat capacity of water (cp(H2O)), change in
temperature of the water (∆TH2O), change in
temperature of the aluminum (∆TAl), and moles of
aluminum (nAl) are all known. The heat (qsurr)
gained by the surroundings (water) can be used to
determine the heat (qsys) lost by the aluminum. This
relationship can be used to determine the molar
heat capacity of aluminum.

Answer 3

Heat is measured through a process called
calorimetry.
Calorimetry relies on the fact that the heat lost by
the system flows into the surroundings.
Therefore, the magnitude of the energy change is
the same for the system and the surroundings, but
the sign of the heat flow is opposite. This is
expressed mathematically as qsys = –qsurr.
Calorimetry can be performed at constant pressure
or at constant volume.
Constant pressure calorimetry involves a simple
experimental setup where the temperature change
of a known amount of water is measured. A
constant pressure calorimeter is not airtight, and
is therefore open to atmospheric pressure, which is
essentially constant.
The heat evolved by a system at constant pressure
is equal to the enthalpy change of that system.
Therefore, constant pressure calorimetry can be
used to determine the enthalpy change of reactions.
Constant pressure calorimetry is also useful for
finding heat capacities. In this example, a known
mass of aluminum was heated to a known
temperature, and then placed in a constant pressure
calorimeter. The change in temperature of the
water (surroundings) was used to calculate the
molar heat capacity of the aluminum.
In this experiment, the moles of water (nH2O), molar
heat capacity of water (cp(H2O)), change in
temperature of the water (∆TH2O), change in
temperature of the aluminum (∆TAl), and moles of
aluminum (nAl) are all known. The heat (qsurr)
gained by the surroundings (water) can be used to
determine the heat (qsys) lost by the aluminum. This
relationship can be used to determine the molar
heat capacity of aluminum.