Calorimeter

Calorimeter
The world’s first ice-calorimeter, used in the winter of 1782-83, by Antoine Lavoisier and Pierre-
Simon Laplace, to determine the heat evolved in various chemical changes; calculations which were
based on Joseph Black’s prior discovery of latent heat. These experiments mark the foundation of
thermochemistry.
A calorimeter is a device used for calorimetry, the science of measuring the heat of chemical
reactions or physical changes as well as heat capacity. The word calorimeter is derived from the Latin
word calor, meaning heat. Differential scanning calorimeters, isothermal microcalorimeters, titration
calorimeters and accelerated rate calorimeters are among the most common types. A simple
calorimeter just consists of a thermometer attached to a metal container full of water suspended above
a combustion chamber.
To find the enthalpy change per mole of a substance A in a reaction between two substances A and B,
the substances are added to a calorimeter and the initial and final temperatures (before the reaction
started and after it has finished) are noted. Multiplying the temperature change by the mass and
specific heat capacities of the substances gives a value for the energy given off or absorbed during the
reaction. Dividing the energy change by how many moles of A were present gives its enthalpy change
of reaction. This method is used primarily in academic teaching as it describes the theory of
calorimetry. It does not account for the heat loss through the container or the heat capacity of the
thermometer and container itself. In addition, the object placed inside the calorimeter show that the
objects transferred their heat to the calorimeter and into the liquid, and the heat absorbed by the
calorimeter and the liquid is equal to the heat given off by the metals.
Adiabatic calorimeters
An Adiabatic calorimeter is a calorimeter used to examine a runaway reaction. Since the calorimeter
runs in an adiabatic environment, any heat generated by the material sample under test causes the
sample to increase in temperature, thus fuelling the reaction.
No adiabatic calorimeter is truly adiabatic - some heat will be lost by the sample to the sample holder.
Examples of adiabatic calorimeters are:-
• THT EV-Accelerating Rate Calorimeter[1]

• HEL Phi-Tec[2]
• A simple Dewar flask
• Systag FlexyTSC[3] a successor of their SIKAREX unit - the electronics of which
could be used to apply a feedback system to heat the sample holder to give a
result closer to true adiabaticy, however as the sample holder is an open ended
glass tube, one soon loses the sample as a great deal of smoke.
Reaction calorimeters
A reaction calorimeter is a calorimeter in which a chemical reaction is initiated within a closed
insulated container. Reaction heats are measured and the total heat is obtained by integrating heatflow
versus time. This is the standard used in industry to measure heats since industrial processes are
engineered to run at constant temperatures. Reaction calorimetry can also be used to determine
maximum heat release rate for chemical process engineering and for tracking the global kinetics of
reactions. There are four main methods for measuring the heat in reaction calorimeter:
Heat flow calorimetry
The cooling/heating jacket controls either the temperature of the process or the temperature of the
jacket. Heat is measured by monitoring the temperature difference between heat transfer fluid and the
process fluid. In addition fill volumes (i.e. wetted area), specific heat, heat transfer coefficient have to
be determined to arrive at a correct value. It is possible with this type of calorimeter to do reactions at
reflux, although the accuracy is not as good.
Heat balance calorimetry
The cooling/heating jacket controls the temperature of the process. Heat is measured by monitoring
the heat gained or lost by the heat transfer fluid.
Power compensation
Power compensation uses a heater placed within the vessel to maintain a constant temperature. The
energy supplied to this heater can be varied as reactions require and the calorimetry signal is purely
derived from this electrical power.
Constant flux
Constant flux calorimetry (or COFLUX as it is often termed) is derived from heat balance calorimetry
and uses specialized control mechanisms to maintain a constant heat flow (or flux) across the vessel
wall.
Bomb calorimeters
A bomb calorimeter is a type of constant-volume calorimeter used in measuring the heat of
combustion of a particular reaction. Bomb calorimeters have to withstand the large pressure within
the calorimeter as the reaction is being measured. Electrical energy is used to ignite the fuel; as the
fuel is burning, it will heat up the surrounding air, which expands and escapes through a tube that
leads the air out of the calorimeter. When the air is escaping through the copper tube it will also heat
up the water outside the tube. The temperature of the water allows for calculating calorie content of
the fuel.
In more recent calorimeter designs, the whole bomb, pressurized with excess pure oxygen (typically
at 30atm) and containing a known mass of sample (typically 1-1.5 g) and a small fixed amount of
water (to absorb produced acid gases), is submerged under a known volume of water (ca. 2000 ml)
before the charge is (again electrically) ignited. The bomb, with sample and oxygen, form a closed
system - no air escapes during the reaction. The energy released by the combustion raises the
temperature of the steel bomb, its contents, and the surrounding water jacket. The temperature change
in the water is then accurately measured. This temperature rise, along with a bomb factor (which is
dependent on the heat capacity of the metal bomb parts) is used to calculate the energy given out by
the sample burn. A small correction is made to account for the electrical energy input, the burning
fuse, and acid production (by titration of the residual liquid). After the temperature rise has been
measured, the excess pressure in the bomb is released.
Basically, a bomb calorimeter consists of a small cup to contain the sample, oxygen, a stainless steel
bomb, water, a stirrer, a thermometer, the dewar (to prevent heat flow from the calorimeter to the
surroundings) and ignition circuit connected to the bomb.

Calorimeter

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Calorimeter

• THT EV-Accelerating Rate Calorimeter[1]

Heat balance calorimetry

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