An investigator records the changes in state and appearance of three different substances when they are heated and then allowed to cool back to room temperature.
| Substance | State and appearance before heating | State and appearance when hot | State and appearance after cooling |
|---|---|---|---|
| Solder alloy | Solid (metallic grey) | Liquid (shiny silver) | Solid (metallic grey) |
| Zinc oxide powder | Solid (white) | Solid (pale yellow) | Solid (white) |
| Raw egg white | Liquid (clear and colourless) | Solid (opaque white) | Solid (opaque white) |
Explain how the observations show that the heating of raw egg white is a chemical change, whereas the heating of zinc oxide powder is a physical change.
