Calcium chloride (CaCl2) is a highly hygroscopic compound. It absorbs water or water vapour from other substances. This process is highly exothermic.
code:
CaCl2 + 2 H2O -> CaCl2·2H2O
Ammonium nitrate (NH4NO3) (nitrate of ammonia) is a strong oxidizing agent. It dissolves in water, but no new products are formed. Ammonium nitrate solutions are used as fertilizers. It is also used in ice cold packs, because when mixed with water, it produces an endothermic reaction, absorbing 25.69 kilojoules of heat per mole of reactant (endothermic enthalpy).
code:
NH4NO3(s) + H2O(l) + energy (heat absorbed) -> NH4NO3(aq) or NH4+(aq) + NO3-(aq)