When Calcium oxide is added to water taken in a beaker, following reaction takes place:
CaO + H2O → Ca(OH)2 + heat
Since the reaction is exothermic, rise in temperature is observed.
When Barium hydroxide is mixed with Ammonium chloride, following reaction takes place:
2NH4Cl + Ba(OH)2 → BaCl2 + 2NH3 + 2H2O
This is an endothermic reaction.Thus, a fall in temperature is observed.