Chemistry / Unit 1: Matter and Measurement
1.2 Physical and Chemical Changes
Notes
A physical change alters the form of a substance but not its identity. A chemical change makes one or more new substances.
- Physical changes: melting, freezing, boiling, dissolving, cutting, crushing.
- Chemical changes: burning, rusting, cooking, digesting, souring of milk.
- Signs of a chemical change: gas bubbles forming, a color change, a new solid (precipitate), light or heat given off, a new odor.
- A chemical property describes how a substance can react, such as flammability or reactivity with acid.
Practice
Which is a chemical change?
Rust is a new substance (iron oxide), so rusting is a chemical change.
Water boiling into steam is a physical change because:
Bubbles can appear in a physical change too. Steam is still water, so no new substance formed.
Which is a chemical property of wood?
Flammability describes how a substance reacts, so it is a chemical property.
Ready for more? Take the Unit 1 test.