ChemistryCLASS 10CBSE
answered 25 May 2026What is a chemical reaction?
A.VERIFIED ANSWERfact-checked by tutors
A chemical reaction is a process in which one or more reactants are converted into one or more products through the breaking and forming of chemical bonds. No atoms are created or destroyed (Law of Conservation of Mass).
Reactants → Products
Example: 2H₂ + O₂ → 2H₂O (Hydrogen + Oxygen → Water)
Types of chemical reactions:
| Type | Description | Example |
|---|---|---|
| Combination (Synthesis) | Two substances combine into one | Iron + Sulfur → Iron Sulfide |
| Decomposition | One substance breaks into two or more | CaCO₃ → CaO + CO₂ |
| Single displacement | One element replaces another | Zinc + HCl → ZnCl₂ + H₂ |
| Double displacement | Two compounds exchange partners | NaCl + AgNO₃ → AgCl + NaNO₃ |
| Combustion | Rapid reaction with oxygen, releasing heat and light | CH₄ + 2O₂ → CO₂ + 2H₂O |
| Redox | Transfer of electrons between reactants | Rusting, burning, cellular respiration |
Signs a reaction has occurred: Color change, gas production (bubbling), temperature change, precipitate formation, change in smell
Energy types:
- Exothermic: Release energy (burning, explosions)
- Endothermic: Absorb energy (photosynthesis, dissolving ammonium nitrate)