* Physical Properties: These are characteristics that can be observed or measured without changing the chemical composition of a substance. Examples include color, density, melting point, and boiling point.
* Chemical Properties: These describe how a substance reacts with other substances, leading to the formation of new substances.
The reaction of sodium and chlorine is a chemical change. It involves the formation of a new substance, sodium chloride (NaCl), which has different properties than either sodium or chlorine. The energy released is a result of the formation of new chemical bonds, indicating a chemical process.
Key Takeaways:
* Chemical reactions involve the formation of new substances and are therefore chemical changes.
* Physical changes only affect the appearance or state of a substance, not its chemical composition.
* Energy release (or absorption) is a common indicator of a chemical reaction.
