Chemical Reactions and Equations Class 10 Notes

These Notes for Class 10 Science Chapter 1 Chemical Reactions and Equations give you a fast, concept-first revision of the whole chapter, built on the latest 2026-27 CBSE syllabus. They cover how to spot a chemical reaction, how to write and balance a chemical equation, and the five reaction types: combination, decomposition, displacement, double displacement and redox, plus corrosion and rancidity.

• Every reaction type explained with a one-line rule, a balanced equation, and the everyday example the CBSE board paper likes to ask.
• Full coverage of balancing by the law of conservation of mass, exothermic vs endothermic reactions, the reactivity series, and oxidation vs reduction.
• Notes aligned with the 2026-27 CBSE Class 10 Science syllabus and written for the board exam; no NEET or JEE references because this is a Class 10 board chapter.

These Collegedunia revision notes are curated by Science subject experts, mapped to the 2026-27 NCERT textbook, and refined against the last five years of CBSE Class 10 Science board papers.

What the Notes for Class 10 Science Chapter 1 Chemical Reactions and Equations Cover

This chapter answers one question: how do substances change into new substances, and how do we write that change down correctly? These notes compress the NCERT order into exam-ready blocks. They cover:

• Spotting a reaction: the five signs, physical vs chemical change, reactants vs products.
• Balancing equations: the law of conservation of mass, the hit-and-trial method, and state symbols (s), (l), (g), (aq).
• The five reaction types: combination, decomposition, displacement, double displacement and redox.
• Everyday oxidation: corrosion (rusting of iron) and rancidity, with prevention methods.

Chemical Reactions: How to Spot One in Class 10 Science

A chemical reaction turns one set of substances into a new set. The substances we start with are the reactants; the new ones formed are the products. We cannot see atoms rearrange, so we watch for these clues:

• Change in state or colour: green ferrous sulphate turns brown; blue copper sulphate fades.
• Evolution of a gas: bubbles rise (zinc with dilute acid gives hydrogen).
• Change in temperature: the test tube feels hot or cold.
• Formation of a precipitate: an insoluble solid settles out.

A word-equation puts reactants on the left, products on the right, joined by an arrow. For burning magnesium, "Magnesium + Oxygen gives Magnesium oxide" becomes Mg + O₂ → MgO (skeletal, not yet balanced).

Physical change versus chemical change

In a physical change no new substance forms and it can usually be reversed; in a chemical change a new substance forms and it is hard to reverse. A common one-mark board question.

Writing and Balancing Chemical Equations in Class 10 Science

A chemical equation is correct only when balanced, resting on the law of conservation of mass: the atoms of each element must be equal on both sides. An equation without equal atoms is skeletal (unbalanced).

Hit-and-trial method, step by step

Balance Fe + H₂O → Fe₃O₄ + H₂, starting with the formula that has the most atoms (Fe₃O₄):

• Step 1. Balance oxygen: 4 O on the right, so put 4 before H₂O.
• Step 2. Balance hydrogen: 8 H on the left now, so put 4 before H₂.
• Step 3. Balance iron: 3 Fe on the right, so put 3 before Fe.
• Step 4. Check: Fe 3 = 3, H 8 = 8, O 4 = 4. Balanced.

Add the physical state after each formula: (s) solid, (l) liquid, (g) gas, (aq) aqueous. Conditions like heat, sunlight or a catalyst go above or below the arrow. For tricky equations, balance metals first, then other non-metals, and leave hydrogen and oxygen for last.

Combination and Decomposition Reactions in Class 10 Science

The first pair are opposites. In a combination reaction many substances join into one; in a decomposition reaction one substance splits into many.

Combination reactions

Two or more reactants combine to form a single product. The classic example is the slaking of quick lime: CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat. Others worth memorising:

• Burning of coal: C(s) + O₂(g) → CO₂(g)
• Whitewash hardening: Ca(OH)₂(aq) + CO₂(g) → CaCO₃(s) + H₂O(l)

Exothermic and endothermic reactions

Reactions that release heat are exothermic; those that absorb energy are endothermic. Respiration is an everyday exothermic reaction: C₆H₁₂O₆(aq) + 6O₂(aq) → 6CO₂(aq) + 6H₂O(l) + energy.

Decomposition reactions

A decomposition reaction is the reverse: a single reactant breaks into two or more products. It needs energy (heat, light or electricity), so these reactions are usually endothermic.

In the electrolysis of water, hydrogen gathers over the cathode and oxygen over the anode, with twice as much hydrogen as oxygen by volume.

Displacement and Double Displacement Reactions in Class 10 Science

In a displacement reaction a more reactive element kicks out a less reactive one from its compound. In a double displacement reaction two compounds trade their ions.

Displacement reactions

An iron nail in blue copper sulphate turns the solution pale and the nail brownish: Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s). The reactivity series decides this: a metal higher up displaces any below it (K, Na, Ca, Mg, Al, Zn, Fe, Pb, Cu).

• Zinc displaces copper: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)

Double displacement and precipitation

When sodium sulphate meets barium chloride, a white precipitate appears at once (a precipitation reaction): Na₂SO₄(aq) + BaCl₂(aq) → BaSO₄(s) + 2NaCl(aq). The two compounds swap partners. This exchange of ions is a double displacement reaction.

Oxidation and Reduction (Redox), Corrosion and Rancidity

Many reactions involve gain or loss of oxygen or hydrogen. These are redox reactions, and the two always happen together. Oxidation = gain of oxygen or loss of hydrogen; reduction = loss of oxygen or gain of hydrogen.

In CuO + H₂ → Cu + H₂O, CuO loses oxygen (reduced) while H₂ gains oxygen (oxidised). A hook is OIL RIG: Oxidation Is Loss, Reduction Is Gain.

Corrosion

Corrosion is a metal being slowly eaten away by moisture, air or acids. The familiar example is the rusting of iron, its slow oxidation in damp air. Rusting needs both oxygen and water together; if either is missing, iron does not rust.

Rancidity

Fats and oils react slowly with oxygen, making food smell and taste bad. This oxidation is rancidity, slowed by antioxidants, airtight containers, nitrogen flushing and refrigeration. Corrosion is the oxidation of a metal; rancidity is the oxidation of fats and oils in food.

Five Reaction Types at a Glance and Exam Practice

This strip lines up the five reaction types with a one-line rule and a balanced example each, to read just before the exam.

For "identify the type of reaction" questions, justify your answer in a few words, e.g. "double displacement, because two compounds exchange ions and a precipitate forms". The reason often carries a separate mark.

Also Check: The full set of CBSE board paper questions for this chapter, with step-by-step answers, is included in the downloadable PDF above, updated for the 2026-27 cycle.

Other Resources for Class 10 Science Chapter 1 Chemical Reactions and Equations

Pair these revision notes with the matching NCERT Solutions, the formula sheet, handwritten notes and the official NCERT book chapter. All resources for Class 10 Science Chapter 1 Chemical Reactions and Equations are linked below.

Notes for Class 10 Science: All Chapters

Related Links: Use the table below to open the revision notes for the other chapters of Class 10 Science. Every chapter ships with the same concept-first notes style, full PDF download, and revision FAQ.