Final answer:
When a wall was painted black, only its physical properties, such as color, changed. This is a physical change, as the chemical composition of the wall itself remains unaffected.
Step-by-step explanation:
When a wall that was once white is painted black, it is physical properties that have changed. This change in the wall's color is a result of a new layer of paint which alters its appearance without affecting the wall's chemical composition. Physical changes involve alterations in the appearance or state of a material without changing its chemical identity.
For example:
- Ice melting is a physical change as water changes from solid to liquid state without altering its chemical structure.
- Mixing chocolate syrup with milk only changes the physical appearance and does not result in a new chemical substance, so it's also a physical change.
- In contrast, chemical properties describe a material's potential to undergo a chemical change to form new substances, such as the flammability of a substance or its reactivity with acids.
Therefore, applying black paint to a wall alters its color—a physical property—and not its chemical nature.