Da VIP Academy / GED / Science / Physical Science
Matter & Chemical Reactions
Distinguish physical and chemical changes and apply conservation of mass.
How it works
Physical vs chemical change
Melting ice, dissolving sugar, and cutting paper are physical — the substance is the same. Rusting, burning, and baking are chemical — new substances form, often with heat, gas, or color change.
Mass is conserved
Atoms are rearranged, never destroyed. If 12 g of carbon reacts fully with 32 g of oxygen, the product must have a mass of 44 g.
Worked examples
A sealed jar of steel wool is burned. Does the total mass change?
- The jar is sealed, so no matter escapes.
- Mass is conserved.
- Total mass stays the same.
Words to know
- Chemical change
- A change that forms new substances.
- Conservation of mass
- Total mass stays constant in a reaction.
Test-day tips
- • If you can reverse it without a new substance, it is physical.