Determination of the heat of combustion of benzoic acid

In experiment C4.3.3.1, the temperature rise in the demonstration calorimeter is measured while burning benzoic acid. The substance is weighed before and after the combustion process. The combustion takes place in an oxygen atmosphere, whereby ignition is initiated by a filament. The energy released is calculated using either a previously determined heat capacity of the filled calorimeter or the individual theoretical values of the heat capacities of the glass jacket and calorimeter liquid. The quantity of heat Q is calculated according to the following formula:

Here DT is the measured temperature difference, m_k and m(H₂O) are the mass of the calorimeter and of the water and C_k and C(H₂O) is the heat capacity of the glass apparatus and the water. In order to calculate the heat of combustion DH, the ignition energy, which also contributed to the heating of the apparatus, must be subtracted and the quantity of heat must be expressed relative to one mol of substance.

Variant (a) is set up in a chemistry board system frame and variant (b) is set up on a base rail.