Explain preparation of ozone.

Explanation

When a slow dry stream of oxygen is passed through a silent electrical discharge, a conversion of oxygen to ozone (10 %) occurs. The product is known as ozonised oxygen.
`3O_2 to 2O_3 DeltaH^(-)` (at 298 K) = +142 kj `mol^(-1)`
Since the formation of ozone from oxygen is an endothermic process, it is necessary to use a silent electrical discharge in its preparation to prevent its decomposition.
If concentrations of ozone greater than 10 percent are required, a battery of ozonisers can be used, and pure ozone (b.p. 101.1 K) can be condensed in a vessel surrounded by liquid oxygen.