Reactants are the starting substances; products are the substances formed. Bonds change, but the counts of each kind of atom stay balanced in this ordinary chemical model. One complete reaction packet uses two hydrogen molecules and one oxygen molecule. If the amounts do not match that ratio, some reactant can be left over.
Matter and chemistry · Discover & try
Can atoms disappear in a chemical reaction?
Reading level 2 of 5 · DevelopingChange
Word help
reactant
A starting substance in a reaction.
product
A substance formed by a reaction.
Watch · Try · Explain
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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