Chemistry · KS3 Y8 · Chemical Reactions
Conservation of mass
Conservation of massFree1:43Heddy Score 3 of 7, below the standard
What you need to know
- Before Lavoisier, burning was explained by an imaginary substance called phlogiston that was supposed to escape.
- Lavoisier showed that oxygen is needed for combustion.
- When something burns in the open its mass seems to fall, because gases escape into the air.
- Burned inside a sealed container, the total mass stays the same: matter is not lost or created in a reaction, which is the law of conservation of mass.
In this clip
Runs 1:43, from 2:28 to 4:11 of the full video.
Heddy ScoreSeven checks every clip must pass before students see it: trusted, on the map, accurate, focused, accessible, safe, and proven by students.3/7, Below the standard
See the seven stars
- Trusted source · passed. The creator's own upload, live and playable here.
- On the map · not judged yet. A teacher watched it: it mainly teaches this map topic.
- Spec-true · not judged yet. Accurate, and right for the current UK specification.
- Focused · passed. One idea, short enough to watch in one go.
- Accessible · passed. Good captions, clear sound and pictures.
- Safe for children · not judged yet. Right for 11 to 16 year olds, with no sales pitch.
- Proven · not judged yet. Earned from our students: they learn from it, find it helpful and watch it to the end.
Our students
Not enough students yet
Our own students' answers. These are what move ★7 Proven.On YouTube
How the Heddy Score works3.01M views · 34.6K likes · CrashCourse 17.3M subscribers
As reported by YouTube on 2026-11-02. Not part of the Heddy Score.Why we picked it
A short, story-led clip showing how careful weighing in a sealed container led Lavoisier to the law of conservation of mass.
CrashCourse on YouTubechecked 2026-10-22
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