# Nitric acid decomposition

I have a problem with the decomposition reaction of Nitric acid($\ce{HNO3}$) by light. My problem: is that reaction is a redox reaction? If it is please tell me the oxidation and reduction (balanced) reactions seperately.

• Why do you think it's photochemical? Nitric acid is sold in clear colorless bottles. – Zhe Jun 30 '17 at 15:27
• @Zhe no, nitric acid is subjected to decomposition due to light. See my answer below. – Nilay Ghosh Jun 30 '17 at 18:34
• Interesting. Never seen the brown bottle before... Thanks! @NilayGhosh – Zhe Jun 30 '17 at 18:39

$$\ce{ 4 HN^{V}O3 → 2 H2O + 4 N^{IV}O2 + O2}$$
The nitrogen dioxide ($\ce{NO2}$) remains dissolved in the nitric acid coloring it yellow or even red at higher temperatures. While the pure acid tends to give off white fumes when exposed to air, acid with dissolved nitrogen dioxide gives off reddish-brown vapors, leading to the common name "red fuming acid" or "fuming nitric acid" – the most concentrated form of nitric acid at Standard Temperature and Pressure (STP). Nitrogen oxides ($\ce{NO_x}$) are soluble in nitric acid.