Nitric acid: oxidation-reduction reactions

Reaction with carbon

A piece of charcoal is heated..

..and introduced in concentrated nitric acid.

A reaction starts,..

and proceeds intensively.

A piece of charcoal is heated..

$C$ $-$ $4e^-$ $+$ $2H_2O$ $\longrightarrow$ $CO_2$ $+$ $4H^+$ $HNO_3$ $+$ $3e^-$ $+$ $3H^+$ $\longrightarrow$ $NO$ $+$ $2H_2O$

$3C$ $+$ $4HNO_3$ $\longrightarrow$ $3CO_2$ $+$ $4NO$ $+$ $2H_2O$