Question

Define exothermic and endothermic changes. Give two examples in each case.

Answer 1

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,
$C+O_2\to {CO}_2+\text{Heat}$
2. Nitrogen combines with oxygen to form nitrogen dioxide. This involves the evolution of heat. That is,
$N_2+O_2\to 2{NO}_2+\text{Heat}$

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,
$C+2S+Heat\to {CS}_2$
2. When mercuric oxide is heated, it decomposes into two elements i.e., mercury and oxygen. That is,
$2HgO+\text{Heat}\to 2Hg+O_2$