6 calorimeter : the next essential is knowledge of the heat capacity of the
calorimeter – this includes the heat capacities of the inner containing vessel ,temperature
measuring instruments, and other surroundings contributing in any measurable way to the
heat changes in the system under observation. All these are included in calorimeter constant
which is the amount of heat required to raise the temperature of the calorimeter by 1
degree (often known as " water equivalent: of the calorimeter).
Two distinct methods can be employed (isothermal and adiabatic)
The first requiring a constant temperature jacket and the second a jacket whose
temperature can be adjusted so that it is the same as the contents of the vessel thus
preventing any heat exchange between the system and its surroundings . in isothermal
calorimetry , corrections must be made for the exchange of heat between the calorimeter
and its suurroundings during the reaction, where this inapplicable to adiabatic calorimetry
,making it more suitable perhaps for high temperature calorimetry where errors due to heat
losses are increased. The drawbacks of adiabatic calorimetry are the difficulties associated
with compensating for sudden changes in temperature in the calorimeter.
The bomb calorimeter is a uesfull pieace of apparatus where the reaction involves a gas
particularly for determination of heat of combustion. The bomb is a strong gas tight steel
vessel in which the material to be oxidized , which may be a liquid or a solid , is placed in a
small crucible supported by thin wires, which may be used to carry the electric current which
ignites the material.Oxygen is pumped into the bomb at up to 25 atm pressure ,and the
bomb is immersed in a clorimeter full of water – all enclosed in aconstant temperature
jacket.the change in temperature of the caolimeter after ignition of the bomb is measured ,
and the apparatus is calibrated using a substance of known heat of combustion or by an
electrical method.heat of reaction involving chlorine and nitrogen have also been
determined by this method.