Calorimeter Definition in Chemistry

A calorimeter is a device used to measure the heat flow of a chemical reaction or physical change. The process of measuring this heat is called calorimetry. A basic calorimeter consists of a metal container of water above a combustion chamber, in which a thermometer is used to measure the change in water temperature. However, there are many types of more complex calorimeters.

The basic principle is that heat released by the combustion chamber increases the temperature of the water in a measurable way. The temperature change may then be used to calculate the enthalpy change per mole of substance A when substances A and B are reacted.

The equation used is:

q = C_v(T_f - T_i )

where:

• q is the amount of heat in joules
• Cv is the calorimeter's heat capacity in joules per Kelvin (J/K)
• T_f and T_i are the final and initial temperatures

Calorimeter History

The first ice calorimeters were built based on Joseph Black's concept of latent heat, introduced in 1761. Antoine Lavoisier coined the term calorimeter in 1780 to describe the apparatus he used to measure heat from guinea pig respiration used to melt snow. In 1782, Lavoisier and Pierre-Simon Laplace experimented with ice calorimeters, in which heat needed to melt ice could be used to measure heat from chemical reactions.

Types of Calorimeters

Calorimeters have expanded beyond the original ice calorimeters.

• Adiabatic calorimeter: Some heat is always lost to the container in an adiabatic calorimeter, but a correction factor is applied to the calculation to compensate for heat loss. This type of calorimeter is used to study runaway reactions.
• Reaction calorimeter: In this type of calorimeter, the chemical reaction occurs within an insulated closed container. Heatflow versus time is measured to arrive at the reaction heat. This is used for reactions intended to run at a constant temperature or to find the maximum heat released by a reaction.
• Bomb calorimeter: A bomb calorimeter is a constant-volume calorimeter, constructed to withstand the pressure produced by the reaction as it heats the air within the container. The temperature change of water is used to calculate the heat of combustion.
• Calvet-type calorimeter: This type of calorimeter relies on a three-dimensional fluxmeter sensor made of rings of thermocouples in series. This type of calorimeter allows for a larger sample size and reaction vessel size, without sacrificing the accuracy of the measurement. An example of a Calvet-type calorimeter is the C80 calorimeter.
• Constant-pressure calorimeter: This instrument measure the enthalpy change of a reaction in solution under conditions of constant atmospheric pressure. A common example of this type of device is the coffee-cup calorimeter.