Physical properties and chemical properties are distinguished by whether or not the substance's chemical identity changes during observation or measurement.

• Physical properties can be observed or measured without changing the substance's chemical identity. These include characteristics such as color, density, mass, volume, melting point, boiling point, hardness, malleability, and electrical conductivity. For example, water's boiling point or the color of copper can be measured without altering what the substance fundamentally is

• Chemical properties describe a substance's ability to undergo a chemical change, meaning the substance's internal structure and chemical identity are altered. These properties can only be observed during a chemical reaction. Examples include flammability, corrosiveness, reactivity with acids, oxidation (like rusting of iron), toxicity, and pH. For instance, iron's tendency to rust in moist air or hydrogen's ability to ignite are chemical properties because they involve forming new substances

In summary, the key distinction is:

• Physical properties do not involve changing the substance's chemical makeup.
• Chemical properties involve the substance's potential to change chemically, producing new substances.

This means physical properties can be measured without a chemical reaction, while chemical properties require a chemical reaction to be observed