4. Types of Reactions
GED® Science: Chemical Reactions & Conservation of Mass (Deep Dive) · preview lesson
Most reactions fit a few recognizable patterns. Knowing the common types helps you predict what happens.
- Synthesis (combination) — two or more substances combine into one: A + B → AB.
- Decomposition — one substance breaks down into two or more: AB → A + B.
- Combustion — a fuel burns in oxygen, releasing energy; for a hydrocarbon fuel the products are carbon dioxide and water: fuel + O₂ → CO₂ + H₂O + energy.
(You may also see replacement reactions, where atoms switch partners.) In every case, atoms are conserved and the equation can be balanced.
⚠️ Common misconception: combustion isn't just 'fire' — it's a chemical reaction with oxygen that releases energy, and burning a hydrocarbon always produces CO₂ and water.
💡 Tip: synthesis = build up; decomposition = break down; combustion = burn with oxygen.
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