Lithium peroxide, Li₂O₂

Addition of alcohol to the aqueous solution obtained by the interaction of hydrogen peroxide and lithium hydroxide precipitates the crystalline product Li₂O₂,H₂O₂,3H₂O, a substance converted by drying over phosphoric anhydride into the anhydrous peroxide, Li₂O₂. The method resembles that employed in the preparation of the peroxides of the alkaline-earth-metals. The combustion of lithium in oxygen yields only a small proportion of peroxide, a distinction from sodium. The peroxide boils at 258° C.

The heat of formation of the peroxide from the monoxide and oxygen is given by the equation

[Li₂O]+(O)=[Li₂O₂]+7.97 Cal.,

the corresponding equations for the peroxides of calcium, strontium, and barium being

[CaO]+(O)=[CaO₂]+4.11 Cal.,
[SrO] + (O)=[SrO₂] + 13.07 Cal.,
[BaO]+(O) =[BaO₂] +18.36 Cal.

In this respect lithium displays close analogy to the alkaline-earth- metals, occupying a position between calcium and strontium. Further analogy is shown by the heat of formation of lithium peroxide from its elements

2[Li] + (O₂)=[Li₂O₂] + 151.29 Cal.,

a value closely approximating to that of calcium peroxide,

[Ca]+(O₂) =[CaO₂] +150.43 Cal.

Divergence from the other alkali-metals is made evident by the fact that sodium peroxide has a considerably lower heat of formation -

2[Na]+(O₂) =[Na₂O₂] +117.69 Cal.