CBSE Class 10 · Science
Chemical Reactions and Equations
Official NCERT chapter from Science (book code jesc1). ExamMaster notes are original teaching at CBSE Class 10 depth.
This lesson follows the official chapter “Chemical Reactions and Equations” in Science. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.
- CBSE Class 10
- Medium level
- 8 concepts
1CHEMICAL EQUATIONS
A chemical equation is a before-and-after write of substances: reactants on the left, products on the right, an arrow for the change. Symbols and counts must name what you started with and what you made. A sentence “it fizzed” is a look, not the equation until the names sit on the arrow.
A pretty arrow with doodle letters is not an equation.
Figure. A chemical equation is a left-to-right sentence: named reactants, one arrow, named product. Burning magnesium is written Mg + O₂ → MgO, then balanced later.
How it works
- Name reactants and productsThe two sides.
- Write the school formulae and the arrowThe equation.
- Keep the look in a second columnEvidence, then the write.
2TYPES OF CHEMICAL REACTIONS
Types of reactions are drawers: combine, split, displace, double-displace, oxidise/reduce — as the lesson named them. A type is a job-pattern, not a brand. One honest example per drawer is enough; a firework photo is a setting.
Forcing every fizz into “combination” is a rush.
Figure. Class 10 sorts reactions by what the arrow does to the pieces: join, split, one swap, or two swaps. The four skeletons are the school test, not four brand names.
How it works
- Watch what happens to the substancesJoin, split, swap…
- Hang the type-name after the jobThe drawer.
- Refuse a type you cannot justifyHonest sort.
3Combination reaction
Combination: two or more become one. A + B → C as the school pattern. Heating hydrogen and oxygen to water (as taught) is this drawer. A split that makes two from one is the next heading.
A mix that stays a mix with no new substance is not this reaction.
Figure. Combination is a join test: two reactants become one product. Quicklime plus water is CaO + H₂O → Ca(OH)₂ — the pieces do not swap partners, they add.
How it works
- Name two (or more) starting substancesThe befores.
- Name one product as taughtThe after.
- Call that combinationJoin-to-one.
4Decomposition reaction
Decomposition: one becomes two or more. C → A + B. Heating a taught carbonate or passing current through water (as the lesson showed) is this drawer. The energy you name (heat, current, light) is the how, not a new type.
A combination written backwards by accident is still a sort you must name honestly.
Figure. Decomposition is a split test: one reactant becomes two products. Heating limestone is CaCO₃ → CaO + CO₂. Heat is the condition on the arrow, not a second reactant.
How it works
- Start with one substanceThe before.
- Name two products as taughtThe split.
- Name heat / current / light only if that was the howDecompose.
5Displacement reaction
Displacement: a more reactive element pushes another out of a compound, as the reactivity story taught. A + BC → AC + B. Iron in a copper-salt solution (as a school look) is this drawer, not a double swap.
Two compounds swapping partners is the next heading.
Figure. Displacement is a one-swap test. Iron enters copper sulphate: Fe + CuSO₄ → FeSO₄ + Cu. The more reactive metal takes the salt; the less reactive metal is pushed out.
How it works
- Name the element and the compoundThe pair.
- See one element in, one element outThe push.
- Call that displacementSingle swap.
6Double displacement reaction
Double displacement: two compounds swap partners, often with a settle-out (precipitate) or a taught acid-base story. AB + CD → AD + CB. A cloudy settle you can name is a look; the swap is the type.
A single element pushing one other is not double.
Figure. Double displacement is a two-swap test. Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl: sulphate joins barium (the precipitate), chloride joins sodium. Both partners move.
How it works
- Name two compoundsThe befores.
- See the partners swapThe double.
- Name a settle or water if the lesson tied itThe look.
7Oxidation and reduction
Oxidation and reduction at this class are a paired job: gain of oxygen / loss of oxygen, or the taught electron-story if the lesson used it — always as a pair. A substance that gains oxygen is oxidised; the partner is reduced, as taught. Redox is the pair-word, not “rust only”.
Saying “it oxidised” with no partner is a half-heading.
Figure. In CuO + H₂ → Cu + H₂O the same oxygen move is two names: CuO loses oxygen (reduction) and H₂ gains oxygen (oxidation). Class 10 redox is this pair, not a half-cell.
How it works
- Name what gained oxygen (or lost electrons) as taughtOxidised.
- Name the partner that did the oppositeReduced.
- Keep them as one pairRedox.
8A balanced equation keeps atoms honest
A balanced equation keeps atoms honest: the same count of each kind on both sides. 2H2 + O2 → 2H2O is honest; H2 + O2 → H2O drops an O and an H. Balancing is counts, not new substances. You may not invent a product to make the counts pretty.
Changing H2O into H2O2 to “fix” oxygen is a new reaction, not a balance.
Figure. A balanced equation keeps each element’s atom count equal on both sides. 2H₂ + O₂ → 2H₂O has four hydrogens and two oxygens left and right. An unbalanced H₂ + O₂ → H₂O fails the oxygen count.
How it works
- Count each element left and rightThe audit.
- Adjust coefficients onlyThe balance.
- Refuse a new formula as a fixHonest atoms.
H2 + O2 → H2O is
- Not balanced — atoms are not honest yet
- Already balanced
- A double displacement
Counts must match; coefficients fix them.
Notes
- Mapped to the official NCERT chapter “Chemical Reactions and Equations”. Original teaching only — no textbook sentences.
- Science here is Physics, Chemistry and Biology ideas at this class, never a language or social-science chapter.
Recap
Hold these pegs from the official chapter “Chemical Reactions and Equations”. The wording is ExamMaster’s teaching, not a textbook recap.
- CHEMICAL EQUATIONS
- A chemical equation is a before-and-after write of substances: reactants on the left, products on the right, an arrow for the change.
- TYPES OF CHEMICAL REACTIONS
- Types of reactions are drawers: combine, split, displace, double-displace, oxidise/reduce — as the lesson named them.
- Combination reaction
- Combination: two or more become one. A + B → C as the school pattern. Heating hydrogen and oxygen to water (as taught) is this drawer. A split that makes two from one is the next heading.
- Decomposition reaction
- Decomposition: one becomes two or more. C → A + B. Heating a taught carbonate or passing current through water (as the lesson showed) is this drawer. The energy you name (heat, current, light) is the how, not a new type.
- Displacement reaction
- Displacement: a more reactive element pushes another out of a compound, as the reactivity story taught.
- Double displacement reaction
- Double displacement: two compounds swap partners, often with a settle-out (precipitate) or a taught acid-base story.
Practise Chemical Reactions and Equations
Reading is free and needs no account. Practice, mocks and progress live in the app.
- A 4-question practice set that ends the chapter
- 1 quick check with worked explanations
- Timed mocks scored with the real marking scheme
- Readiness tracked per topic, kept on your device