Heat and water absorption by calcium chloride
Anhydrous calcium chloride is an effective desiccant, but the absorption of water by anhydrous calcium chloride is exothermic; i.e. the reaction releases heat.

$$\ce{CaCl2 + 6 H2O -&gt; CaCl2 . 6 H2O}\quad\Delta H = -97\ \mathrm{kJ/mol}$$