Chemistry

Ozone is a powerful oxidizing agent, far better than dioxygen. It is also unstable at high concentrations, decaying to ordinary diatomic oxygen (in about half an hour in atmospheric conditions):^[9]

2 O₃ → 3 O₂

This reaction proceeds more rapidly with increasing temperature and decreasing pressure. Deflagration of ozone can be triggered by a spark, and can occur in ozone concentrations of 10 wt% or higher.^[10]

Metals

Ozone will oxidize metals (except gold, platinum, and iridium) to oxides of the metals in their highest oxidation state. For example:

2 Cu⁺ (aq) + 2 H₃O⁺ (aq) + O₃ (g) → 2 Cu²⁺ (aq) + 3 H₂O (l) + O₂ (g)

Non-metals

Ozone also increases the oxidation number of oxides, such as the oxidation of nitric oxide to nitrogen dioxide:

NO + O₃ → NO₂ + O₂

This reaction is accompanied by chemiluminescence. The NO₂ can be further oxidized:

NO₂ + O₃ → NO₃ + O₂

The NO₃ formed can react with NO₂ to form N₂O₅:

NO₂ + NO₃ → N₂O₅

Ozone reacts with carbon to form carbon dioxide, even at room temperature:

C + 2 O₃ → CO₂ + 2 O₂

Ozone does not react with ammonium salts but it reacts with ammonia to form ammonium nitrate:

2 NH₃ + 4 O₃ → NH₄NO₃ + 4 O₂ + H₂O

Ozone reacts with sulfides to make sulfates. For example, lead(II) sulfide is oxidised to lead(II) sulfate:

PbS + 4 O₃ → PbSO₄ + 4 O₂

Sulfuric acid can be produced from ozone, starting either from elemental sulfur or from sulfur dioxide:

S + H₂O + O₃ → H₂SO₄

3 SO₂ + 3 H₂O + O₃ → 3 H₂SO₄

All three atoms of ozone may also react, as in the reaction of tin(II) chloride with hydrochloric acid and NaCl:

3 SnCl₂ + 6 HCl + O₃ → 3 SnCl₄ + 3 H₂O

In the gas phase, ozone reacts with hydrogen sulfide to form sulfur dioxide:

H₂S + O₃ → SO₂ + H₂O

In an aqueous solution, however, two competing simultaneous reactions occur, one to produce elemental sulfur, and one to produce sulfuric acid:

H₂S + O₃ → S + O₂ + H₂O

3 H₂S + 4 O₃ → 3 H₂SO₄

Iodine perchlorate can be made by treating iodine dissolved in cold anhydrous perchloric acid with ozone:

I₂ + 6 HClO₄ + O₃ → 2 I(ClO₄)₃ + 3 H₂O

Solid nitryl perchlorate can be made from NO₂, ClO₂, and O₃ gases:

2 NO₂ + 2 ClO₂ + 2 O₃ → 2 NO₂ClO₄ + O₂

Combustion

Ozone can be used for combustion reactions and combusting gases; ozone provides higher temperatures than combusting in dioxygen (O₂). The following is a reaction for the combustion of carbon subnitride which can also cause lower temperatures:

3 C₄N₂ + 4 O₃ → 12 CO + 3 N₂

Ozone can react at cryogenic temperatures. At 77 K (-196 °C), atomic hydrogen reacts with liquid ozone to form a hydrogen superoxide radical, which dimerizes:^[11]

H + O₃ → HO₂ + O

2 HO₂ → H₂O₄

Ozonides

Ozonides can be formed, which contain the ozonide anion, O₃⁻. These compounds are explosive and must be stored at cryogenic temperatures. Ozonides for all the alkali metals are known. KO₃, RbO₃, and CsO₃ can be prepared from their respective superoxides:

KO₂ + O₃ → KO₃ + O₂

Although KO₃ can be formed as above, it can also be formed from potassium hydroxide and ozone:^[12]

2 KOH + 5 O₃ → 2 KO₃ + 5 O₂ + H₂O

NaO₃ and LiO₃ must be prepared by action of CsO₃ in liquid NH₃ on an ion exchange resin containing Na⁺ or Li⁺ ions:^[13]

CsO₃ + Na⁺ → Cs⁺ + NaO₃

Treatment with ozone of calcium dissolved in ammonia leads to ammonium ozonide and not calcium ozonide:^[11]

3 Ca + 10 NH₃ + 6 O₃ → Ca·6NH₃ + Ca(OH)₂ + Ca(NO₃)₂ + 2 NH₄O₃ + 2 O₂ + H₂

Applications

Ozone can be used to remove manganese from water, forming a precipitate which can be filtered:

2 Mn²⁺ + 2 O₃ + 4 H₂O → 2 MnO(OH)₂ (s) + 2 O₂ + 4 H⁺

Ozone will also turn cyanides to the one thousand times less toxic cyanates:

CN^- + O₃ → CNO⁻ + O₂

Finally, ozone will also completely decompose urea:^[14]

(NH₂)₂CO + O₃ → N₂ + CO₂ + 2 H₂O