Physical Science / Unit 2: Properties and States of Matter
2.2 Physical and Chemical Changes
Notes
- In a physical change the substance keeps its identity. Examples: cutting, crushing, melting, dissolving, boiling.
- In a chemical change (chemical reaction) new substances form. Examples: burning, rusting, baking, digesting food.
- Signs of a chemical change: gas bubbles, a color change, a precipitate (new solid), light or heat given off, a new odor.
- A change of state is physical, and it can be reversed by changing temperature. Many chemical changes cannot be easily reversed.
Practice
Which is a chemical change?
Rust is iron oxide, a new substance.
A student heats a white powder and it gives off a gas and turns black. This is most likely:
Gas production and color change are signs of a new substance.
Which is a physical change?
Steam is still water ($\text{H}_2\text{O}$).
Ready for more? Take the Unit 2 test.