A reaction in which heat is given out is called exothermic reactions. In an exothermic reaction, energy is released.
Two examples of exothermic reactions:
1. When carbon burns in oxygen to form carbon dioxide, a lot of heat is produced. That is,
C+O2→CO2+ Heat
2. Nitrogen combines with oxygen to form nitrogen dioxide. This involves the evolution of heat. That is,
N2+O2→2NO2+ Heat
A reaction in which heat is absorbed is called an endothermic reaction. In an endothermic reaction, energy is absorbed.
Two examples of endothermic reactions:
1. When carbon is heated with sulphur at high temperature, liquid carbon disulphide is formed. That is,
C+2 S+Heat→CS2
2. When mercuric oxide is heated, it decomposes into two elements i.e., mercury and oxygen. That is,
2HgO+ Heat →2Hg+O2