A chemical reaction can rearrange atoms into new groups, but it does not make those atoms disappear. In this model, two hydrogen pairs and one oxygen pair can make two water groups. Count hydrogen and oxygen before and after. Extra starting groups can remain when there is not enough of the other reactant.
Matter and chemistry · Discover & try
Can atoms disappear in a chemical reaction?
Reading level 1 of 5 · EarlyChange
Word help
reactant
A starting substance in a reaction.
product
A substance formed by a reaction.
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See how it works
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Virtual atom bookkeeping only; no gas mixing, ignition, reaction-rate or laboratory procedure is modelled.
What to look for
- Each element count is conserved
- Molecule counts can change
- An excess reactant can remain
Explain what you noticed
There are 3 H2 groups and 2 O2 groups. After one complete 2 H2+O2 packet reacts, what remains unused?
Keep this idea: Count each element before and after rearranging the groups.
Follow the sources
- American Chemical Society — What Is a Chemical Reaction?
- American Chemical Society — Controlling the Amount of Products
Source material checked 2026-10-28. Explanations and activities by Nepedia. Source links do not imply endorsement.
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