Chemistry

Compresses and heat of dissolution


An important application for dissolving heat is emergency pads, which are for sale in many countries.

They are used as first aid in the bruises suffered, for example during the practice of physical exercises, sports.

Hot compress is a plastic bag with a water ampoule and a dry chemical (calcium chloride or magnesium sulfate).

With a knock, the ampoule breaks and the water dissolves the chemical, releasing heat:

CaCl2(S) + water → CaCl2(aq) ∆H = -82.7kJ / mol

The cold compress contains an endothermic dissolving chemical (such as ammonium nitrate).

NH4AT THE3(S) + water → NH4AT THE3(aq) ΔH = + 26.3kJ / mol

These pads are not reusable and their effect lasts about 30 minutes.