Physical vs chemical changes

Science · Matter & Materials · ages 11-13

Name ______________________ Date ____________

You mix two clear liquids. Bubbles form and the container gets warm. What best describes what's happening?
- A physical change, because nothing solid appeared
- A chemical change, likely making new substances
- An irreversible change, but not physical or chemical
Which of these is a physical change?
- Iron rusting in the rain
- Ice melting into water
- Wood burning in a fire
If you burn a piece of paper inside a sealed container so no gas can escape, the total mass inside stays the same before and after burning.
Circle one: True False
You add one clear liquid to another clear liquid, and a cloudy white solid immediately settles at the bottom. What does this show?
- A precipitate formed: a chemical change
- The liquids just dissolved into each other
- The liquids froze because they got cold
Why is dissolving sugar in tea a physical change, while burning toast is a chemical change?
- Dissolving is slower than burning
- Dissolving keeps the sugar as sugar, but burning turns the bread into different substances
- Burning only happens to food, and dissolving only happens to solids in water
A candle has a mass of 50 g. It burns for an hour. The wax and soot left behind have a mass of 12 g. How many grams of the candle's own matter went into the air as gas?
Answer: ______________
A steel nail can bend or it can rust. Which pairing correctly matches each change?
- Both bending and rusting are physical changes
- Bending is chemical; rusting is physical
- Bending is physical; rusting is chemical
A piece of steel wool has a mass of 5 g. After it burns completely in oxygen, the iron oxide formed has a mass of 7 g. How many grams of oxygen from the air combined with the iron?
Answer: ______________

Answer key

For grown-ups. Fold this page away before handing over the rest.

Physical vs chemical changes W1-mt_1hgck6ucII-s1

A chemical change, likely making new substances · Bubbles and a temperature change are signs that new substances are forming, which makes this a chemical change.
Ice melting into water · Melting only changes ice's state to liquid. It's still water, so no new substance formed.
True · Mass is conserved: the atoms in the paper rearrange into ash and gases, but none are created or destroyed.
A precipitate formed: a chemical change · A solid appearing out of two clear liquids is called a precipitate, and it's a strong sign a new substance has formed.
Dissolving keeps the sugar as sugar, but burning turns the bread into different substances · You can evaporate the tea to get the sugar back, but burnt toast can never turn back into bread because new substances were made.
38 · 50 - 12 = 38 g of the candle's matter left as gas. The gases weigh even more than that, because oxygen from the air joined in.
Bending is physical; rusting is chemical · Bending only reshapes the same iron atoms. Rusting reacts the iron with oxygen to form a new substance, iron oxide.
2 · Mass is still conserved. The extra 2 g came from oxygen gas joining with the iron to form iron oxide, so the product weighs more than the metal alone.