Chemistry · Chapter 06
💥 Chemical Reactions
What happens when atoms meet.
💡 When Atoms Rearrange
A chemical reaction happens when atoms break old bonds and form new ones — producing new substances. The starting materials are reactants; what comes out is products.
The Law of Conservation of Mass: atoms are never created or destroyed in a reaction — only rearranged. That's why we balance equations.
2H₂ + O₂ → 2H₂O
Common reaction types:
• Combination — A + B → AB
• Decomposition — AB → A + B
• Displacement — A + BC → AC + B
• Combustion — Fuel + O₂ → CO₂ + H₂O + Heat
Thermite reaction — highly exothermic redox reactionWikimedia Commons / CC BY-SA 3.0
Iron rusting — slow oxidation (corrosion) in moist airWikimedia Commons / CC BY-SA 3.0
🎬
Hydrogen Burns to Make Water
AnimationHydrogen molecules meet oxygen, atoms break apart, then recombine as water — releasing heat.
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Identify the Reaction Type
ExperimentPick a reaction — see what type it is and what's happening.
TypeCombination
Two or more substances combine to form one product. Hydrogen and oxygen combine into water.