Bomb Calorimetry (Constant Volume) (6.3.2) Flashcards
• A bomb calorimeter (constant volume calorimeter) is a steel container within a second steel container; the calorimeter is sealed and held at constant volume.
• A bomb calorimeter (constant volume calorimeter) is a steel container within a second steel container; the calorimeter is sealed and held at constant volume.
• Constant volume calorimetry is useful for finding the change in internal energy (∆E) for chemical reactions.
• Constant volume calorimetry is useful for finding the change in internal energy (∆E) for chemical reactions.
A bomb calorimeter (constant volume calorimeter) is
constructed from a steel “bomb” within a second
steel container. This construction allows for the
measurement of heat at constant volume.
The heat capacity of the calorimeter and its
contents must be considered when performing
bomb calorimetry calculations. The heat capacity of
the calorimeter and its contents is the sum of the
heat capacity of the calorimeter (Ccalorimeter) and the
molar heat capacity at constant volume for water
(cv) multiplied by the moles of water present in the
calorimeter.
Constant volume calorimetry is useful for finding the
change in internal energy (∆E) for chemical
reactions.
Problem: 2.84 g ethanol (CH3CH2OH) is burned in
excess oxygen in a bomb calorimeter. The
temperature of the calorimeter changes from
25.00˚C to 33.73˚C. If the heat capacity of the
calorimeter and its contents (C) is 9.63 kJ/˚C, what
is the value of q for burning 1.00 mol ethanol at
constant volume and 25.00˚C?
Calorimetry relies on the equality qsys = –qsurr. In
other words, the heat given off by the system is
absorbed by the surroundings (the calorimeter).
The heat of the surroundings is equal to the heat
capacity of the calorimeter and its contents (C)
multiplied by the change in temperature (∆T, or Tf –
Ti). Using these values, the heat of the system is
found to be –84.1 kJ—the reaction is exothermic.
Dividing this value by the moles of ethanol present
(6.17 x 10–2 mol) yields the heat for the combustion
of 1 mol ethanol at constant volume and 25.00˚C
(–1.36 x 103
kJ/mol).
The heat at constant volume (qv) is equal to the
change in internal energy (∆E) for the reaction.
Therefore, ∆E = –1.36 x 103
kJ/mol for the
combustion of ethanol at 25.00˚C.
A bomb calorimeter (constant volume calorimeter) is
constructed from a steel “bomb” within a second
steel container. This construction allows for the
measurement of heat at constant volume.
The heat capacity of the calorimeter and its
contents must be considered when performing
bomb calorimetry calculations. The heat capacity of
the calorimeter and its contents is the sum of the
heat capacity of the calorimeter (Ccalorimeter) and the
molar heat capacity at constant volume for water
(cv) multiplied by the moles of water present in the
calorimeter.
Constant volume calorimetry is useful for finding the
change in internal energy (∆E) for chemical
reactions.
Problem: 2.84 g ethanol (CH3CH2OH) is burned in
excess oxygen in a bomb calorimeter. The
temperature of the calorimeter changes from
25.00˚C to 33.73˚C. If the heat capacity of the
calorimeter and its contents (C) is 9.63 kJ/˚C, what
is the value of q for burning 1.00 mol ethanol at
constant volume and 25.00˚C?
Calorimetry relies on the equality qsys = –qsurr. In
other words, the heat given off by the system is
absorbed by the surroundings (the calorimeter).
The heat of the surroundings is equal to the heat
capacity of the calorimeter and its contents (C)
multiplied by the change in temperature (∆T, or Tf –
Ti). Using these values, the heat of the system is
found to be –84.1 kJ—the reaction is exothermic.
Dividing this value by the moles of ethanol present
(6.17 x 10–2 mol) yields the heat for the combustion
of 1 mol ethanol at constant volume and 25.00˚C
(–1.36 x 103
kJ/mol).
The heat at constant volume (qv) is equal to the
change in internal energy (∆E) for the reaction.
Therefore, ∆E = –1.36 x 103
kJ/mol for the
combustion of ethanol at 25.00˚C.
