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# Why ZnO is yellow at high temperature?

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## Zinc oxide$\mathrm{ZnO}$ is generally white in color.When $\mathrm{ZnO}$ is heated above $800°\mathrm{C}$ , it loses some of the Oxygen (${\mathrm{O}}_{2}$) reversibly. This results in the yellow color of $\mathrm{ZnO}$ as it absorbs the blue wavelength of light, thus reflecting a yellow colour.However, $\mathrm{ZnO}$ changes from yellow to white colour after cooling down.Chemical ReactionThe above reaction is shown below:$\mathrm{ZnO}\left(\mathrm{s}\right)\stackrel{∆}{⇌}{\mathrm{Zn}}^{2+}\left(\mathrm{s}\right)+\frac{1}{2}{\mathrm{O}}_{2}\left(\mathrm{g}\right)+2{\mathrm{e}}^{-}$(Zinc oxide)

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