Determination of enthalpy of chemical reactions

Determination of enthalpy of chemical reactions by Differential Scanning Calorimeter (DSC)

One main application of DSC is the determination of reaction enthalpies of chemical reactions and also of transformations like melting points and phase transitions.

Enthalpy means the amount of energy that is released or consumed by a process in form of heat release or heat uptake to or from the environment.

There are two types of enthalpy that can be distinguished by their algebraic sign: exothermic processes where energy is released from a system show negative enthalpy and endothermic processes where energy is consumed by a system show positive enthalpy.

An example for an endothermic process is the melting, where heat energy is needed to break the crystal structure of a solid and transfer it into a fluid phase. An example for an exothermic reaction is a simple burning process where a substance reacts with oxygen under the release of heat.

Considering a chemical reaction on the DSC, the sample temperature is measured together with the temperature of an (usually empty) reference crucible that is placed in the same atmosphere and temperature field. If there is a rise or decrease of the sample temperature, compared to the reference, a reaction is taking place. In the evaluation, the difference between reference and sample is calculated, what leads to the measurement curve that contains positive or negative peaks at the points where the temperature of reference and sample are different. The integration of the peak area gives the amount of energy that is released or consumed.