Identify the endothermic and exothermic reaction: 2KClO3(s) → 2KCl(s) + 3O2 (on heating)

Endothermic reaction (as expected in the textbook).

The symbol \(\Delta\) above the arrow shows that heat has to be supplied to potassium chlorate to make it decompose into potassium chloride and oxygen. Because the reaction takes place only when heat is absorbed from the burner, it is classed as an endothermic (thermal decomposition) reaction.

Note: strictly, the measured enthalpy change for this decomposition is slightly negative; heat is needed mainly to start it at a useful rate. For the board exam, write "endothermic".