Copper oxide and zinc, undergoing an exothermic displacement reaction. The reaction is self- perpetuating after being initially lit, since it provides its own heat energy needed for the reaction to continue. Reactions that give off heat are known as exothermic. A displacement reaction is when an element is displaced from its compound (copper oxide, CuO) by a more reactive element (zinc, Zn), to produce the element in its pure form (copper metal, Cu) and a new compound (zinc oxide, ZnO). The zinc oxide is seen as a yellow powder (centre, left) which turns white when cool.