Editing Calorimeter (section)

==Adiabatic and Isoperibol calorimeters==

Sometimes referred to as '''constant-pressure calorimeters''', adiabatic calorimeters measure the change in [[enthalpy]] of a reaction occurring in [[Solution (chemistry)|solution]] during which the no heat exchange with the surroundings is allowed ([[adiabatic]]) and the [[atmospheric pressure]] remains constant.

An example is a coffee-cup calorimeter, which is constructed from two nested [[Styrofoam]] cups, providing insulation from the surroundings, and a lid with two holes, allowing insertion of a thermometer and a stirring rod. The inner cup holds a known amount of a solvent, usually water, that absorbs the heat from the reaction. When the reaction occurs, the outer cup provides [[Thermal insulation|insulation]]. Then

: <math>C_\text{p} = \frac {W\Delta H}{M\Delta T}</math>

where

:<math>C_\text{p}</math>, Specific heat at constant pressure
:<math>\Delta H</math>, Enthalpy of solution
:<math>\Delta T</math>, Change in temperature
:<math>W</math>, mass of solvent
:<math>M</math>, molecular mass of solvent

The measurement of heat using a simple calorimeter, like the coffee cup calorimeter, is an example of constant-pressure calorimetry, since the pressure (atmospheric pressure) remains constant during the process. Constant-pressure calorimetry is used in determining the changes in enthalpy occurring in solution. Under these conditions the change in enthalpy equals the heat.

Commercial calorimeters operate in a similar way. The semi-adiabatic (isoperibol) calorimeters measure temperature changes up to 10{{sup|−6}}{{nbsp}}°C and account for heat loss through the walls of the reaction vessel to the environment, hence, semi-adiabatic. The reaction vessel is a dewar flask which is immersed in a constant temperature bath. This provides a constant heat leak rate that can be corrected through the software. The heat capacity of the reactants (and the vessel) are measured by introducing a known amount of heat using a heater element (voltage and current) and measuring the temperature change.

Adiabatic calorimeters most commonly used in materials science research to study reactions that occur at a constant pressure and volume. They are particularly useful for determining the heat capacity of substances, measuring the enthalpy changes of chemical reactions, and studying the thermodynamic properties of materials.