The big picture
Every idea here is one rule and one equation.
| Idea | Remember | Example |
|---|---|---|
| New substance | Reactants in, products out | magnesium ribbon → white powder |
| Words to formulae | Word sentence, then formulae | H₂ + O₂ → H₂O |
| Balancing | Each atom's count must match | 2H₂ + O₂ → 2H₂O |
| Combination | Many reactants join into one; some give out heat | C + O₂ → CO₂ |
| Decomposition | One reactant splits into many; the splits here take in energy | CaCO₃ → CaO + CO₂ |
| Displacement | A free element swaps in | Zn + CuSO₄ → ZnSO₄ + Cu |
| Double displacement | Two compounds swap partners; cross the charges, cut down; a solid is a precipitate | CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄ |
| Redox | Gain oxygen = oxidised; lose = reduced | CuO + H₂ → Cu + H₂O |
| Slow reactions | Remove air or water, it slows | rusting needs both |
Write a change with symbols. Then read its shape: one product, many products, or a swap.
Open Chapter 1 in your Class 10 book, Science. It goes further into each shape and its heat change.