Chemical reactions
which can be initiated
using a spark can be
carried out in a device
called a bomb
calorimeter. Usually
heats of combustion
are measured this way.
The substance to be burned is massed into
the “bomb, which is fitted with a device
that can deliver a spark and with a tube
that can deliver oxygen under pressure.
The bomb is then sealed and immersed in
a well-insulated vat of water.
Oxygen is let into the bomb, the spark
generated, the reaction occurs, and no
products escape as the heat is generated.
The heat warms the bomb and thus the
water surrounding it.
The “stuff” absorbing the heat is not only
the water, but also anything immersed in
it.
It includes the thermometer and the stirrer
which ensures that any heat is uniformly
distributed before the final temperature is
read.
Before a bomb calorimeter is used its specific
heat capacity must be determined.
Sample Problem
A 1.32 g sample of sucrose, C12H22O11 is
burned in the presence of excess oxygen in a
bomb calorimeter. The heat capacity of the
calorimeter is 9.43 kJ/oC. The heat liberated
by the combustion in the bomb caused the
temperature of the calorimeter’s contents to
change from 25.00 oC to 27.32 oC. Calculate
the heat of combustion per mole of sucrose in
units of kJ/mol.