* Physical Changes: Alter the form or appearance of a substance but don't change its chemical composition.
* Chemical Changes: Result in the formation of new substances with different chemical properties.
What happens when you heat sodium chloride?
* Melting: Sodium chloride melts at a high temperature (801°C). The solid crystal structure breaks down, but the chemical bonds between sodium and chlorine remain intact.
* Boiling: At even higher temperatures, sodium chloride boils. The molten salt changes to a gaseous state, but again, the chemical composition (NaCl) stays the same.
Key Point: Although the state of the sodium chloride changes (solid to liquid to gas), the chemical formula (NaCl) remains the same. No new substances are formed.
