Colour change, an apple that has turned brown has undergone chemical change, so its colour changes.
Energy changes, whether released or absorbed, like fireworks, as it releases energy in the form of light that can be seen.
Odour changes, when food spoils, they undergo chemical changes. Like the egg, if it is rotten they smell differently from fresh eggs. Production of gases or solids from the chemical changes, when wood is burned, they turn into ashes and gases, and it can’t be reversed, thus it is a chemical change.
And chemical changes are not easily reversed, unlike physical reactions. Think about ice for a moment. After ice melts into liquid water, you can refreeze it into solid ice if the temperature drops. Freezing and melting are physical changes. The substances produced during chemical changes however cannot easily change back into the original substances. The most important thing for you to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.