What does one mean by exothermic and endothermic reactions? Give examples.
[2 Marks]

The chemical reactions that release heat energy are called exothermic reactions.
[0.5 Marks]
Example: $\text{C(s)}+{\text{O}}_2\text{(g)}\to {\text{CO}}_2\text{(g)}+\text{Heat Energy}$
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The chemical reactions in which heat energy is absorbed are called endothermic reactions.
[0.5 Marks]
Example: ${\text{CaCO}}_3\left(s\right)\stackrel{\text{Heat}}{\to }\text{CaO(s)}+{\text{CO}}_2\left(g\right)$
[0.5 Marks]