Chapter 3 · Matter and Energy
3.5Differences in Matter: Physical and Chemical Properties
9 min · two checks
Predict
Is “iron rusts in moist air” a physical property or a chemical property?
The idea
- Classify properties as physical or chemical.
- Use a property to tell two substances apart.
A physical property can be observed without changing the substance into something else. Color, density, melting point, boiling point, odor, solubility, and hardness are physical. You can measure the boiling point of ethanol and still have ethanol afterward. A chemical property describes a possible chemical change: flammability, the tendency to rust, the tendency of an acid to react with a base.
Properties are how you identify a substance when appearance is not enough. Diamond and graphite are both carbon, but their physical properties differ because the atoms are arranged differently. Sodium chloride and sucrose are both white crystals; solubility, melting behavior, and what happens when each is heated strongly will tell them apart. When you record a property, record the conditions if they matter — density depends on temperature, solubility often does too.
Keep these
- Physical properties do not change chemical identity.
- Chemical properties describe how a substance reacts.
- Identification uses a set of properties, not color alone.