Oxygen evolution

Oxygen evolution is the process of generating molecular oxygen (O2) by a chemical reaction, usually from water. Oxygen evolution from water is effected by oxygenic photosynthesis, electrolysis of water, and thermal decomposition of various oxides. The biological process supports aerobic life. When relatively pure oxygen is required industrially, it is isolated by distillation of liquified air.Photosynthetic oxygen evolution is the fundamental process by which oxygen is generated in earth's biosphere. The reaction is part of the light-dependent reactions of photosynthesis in cyanobacteria and the chloroplasts of green algae and plants. It utilizes the energy of light to split a water molecule into its protons and electrons for photosynthesis. Free oxygen, generated as a by-product of this reaction, is released into the atmosphere.Together with hydrogen (H2), oxygen is evolved by electrolysis of water. Chemical oxygen generators consist of chemical compounds that release O2 upon some stimulation, usually heat. They are used in submarines and commercial aircraft, providing emergency oxygen. Oxygen is generated by high-temperature decomposition of sodium chlorate: