Conservation of Mass in Reactions
📋 What it is
In a reaction, atoms are never created or destroyed — mass before equals mass after.
🗣️ Coach says
Here’s the big rule: atoms just rearrange, they don’t vanish. So if you could weigh everything (including any gas) before and after a reaction, the totals match exactly. When wood “disappears” into ash and smoke, the mass didn’t vanish — it left as gases.
🧠 Memory hook
Atoms are never lost, only rearranged. Mass before = mass after.
😂 Giggle
Why did oxygen go on a date with potassium?
Because their relationship was OK!
😲 Whoa!
When a log burns down to a tiny pile of ash, almost all its mass didn’t vanish — it floated away as invisible carbon dioxide and water vapour.
✅ Quick check: A log burns to a small pile of ash. Where did most of its mass go?
Say your answer out loud first — then reveal.
It left as gases (carbon dioxide and water vapour); mass wasn’t destroyed — it just changed form and floated away.
Conservation of mass: atoms are conserved, so the “missing” mass escaped as gas.
🪄 Trick question: Does burning DESTROY matter because things get smaller?
Careful — think it through, then reveal.
No — burning rearranges atoms into gases that escape; the matter is conserved, just spread out and invisible.
Matter is never destroyed in a reaction, only transformed.
🧪 Try it! (2 minutes)
Picture a sealed jar with a reaction inside. Its total weight wouldn’t change — nothing can escape, so mass is conserved.