Are all reactions reversible?

Reversible Reaction:

1. A reaction that can take place in both forward and backward direction is called Reversible reaction.
2. Example: Reaction of Nitrogen$\left({\mathrm{N}}_2\right)$ and Oxygen$\left({\mathrm{O}}_2\right)$: ${\mathrm{N}}_2\left(\mathrm{g}\right)+{\mathrm{O}}_2\left(\mathrm{g}\right)\rightleftharpoons 2\mathrm{NO}\left(\mathrm{g}\right)$

Irreversible reaction:

1. Reactions that can occur in the forward direction only is called Irreverisble Reaction.
2. Example: Reaction of sodium$\left(\mathrm{Na}\right)$ with water$\left({\mathrm{H}}_2\mathrm{O}\right)$: $2\mathrm{Na}\left(\mathrm{s}\right)+2{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right)\to 2\mathrm{NaOH}\left(\mathrm{aq}\right)+\hspace{0.17em}{\mathrm{H}}_2\left(\mathrm{g}\right)$ Combustion of Hydrocarbons: ${\mathrm{C}}_{\mathrm{x}}{\mathrm{H}}_{\mathrm{y}}+\left(\mathrm{x}+\frac{\mathrm{y}}{4}\right){\mathrm{O}}_2\to {\mathrm{xCO}}_2+\frac{\mathrm{y}}{2}{\mathrm{H}}_2\mathrm{O}$

Thus, all reactions are not reversible in nature.