Today is rung 4 of 4 on this topic
Atoms, molecules and chemical reactions
Can do: Explains that reactions rearrange atoms rather than creating or destroying them, and identifies evidence of a reaction.
Why it matters
Conservation of mass and rearrangement is the core of chemistry, and it's the idea that makes balancing equations sensible later.
What it looks like when it's wobbly
Thinks new atoms are made in a reaction, and can't distinguish a chemical change from a physical one.
⏱️ Two-minute check
"Where do the atoms in a burnt log go? Name three signs a chemical reaction happened."
Solid looks like: Into gases and ash, nothing destroyed; gas, colour change, temperature change, new substance.
The full activity for this topic · 25 minutes
Sealed Reaction
- 1Weigh the sealed bag with the reagents separate inside, then mix and reweigh. Mass unchanged.
- 2Note the evidence: gas, cold to the touch, fizzing.
- 3Open the bag and reweigh — now it's lighter. Explain exactly why.
- 4Make a red cabbage indicator and test household liquids for acid and alkali.
- 5Write a word equation for the reaction.
If it's too hard
Just the sealed-bag mass demonstration with a prediction.
If it's too easy
Count atoms on each side of a simple equation and balance it.
Say this
"Nothing was created and nothing was destroyed. So where exactly did the mass go when you opened it?"