Question 9
What does one mean by exothermic and endothermic reactions? Give examples.

The chemical reactions that release heat energy are called exothermic reactions.
Example: $\text{C(g)}+{\text{O}}_2\text{(g)}\to {\text{CO}}_2\text{(g)}+\text{Heat Energy}$

The chemical reactions in which heat energy is absorbed are called endothermic reactions.
Example: ${\text{CaCO}}_3\stackrel{\text{Heat}}{\to }\text{CaO}+{\text{CO}}_2$