Is heating zinc oxide a physical or chemical change?
Zinc oxide is a white powder. When heated strongly (above 800°C) it turns yellow but becomes white again when cold.
What happens is that the zinc oxide loses some of its oxygen when it is hot but this reaction is reversed on cooling.
The hot zinc oxide absorbs some of the blue wavelengths of light making the reflected light look more yellow.
The loss of oxygen makes it a reversible chemical change.