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By rohit.pandey1
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Updated on 25 Jun 2026, 14:58 IST
Chemical Reactions and Equations is the first chapter of CBSE Class 10 Science. It introduces students to how chemical changes happen, how reactions are written in the form of equations, and why equations must be balanced. This chapter is important because it builds the base for Chemistry topics such as acids, bases, salts, metals, non-metals, carbon compounds, oxidation, reduction, corrosion, and daily-life chemical processes.
These Chemical Reactions and Equations Class 10 Notes are prepared for quick revision and board exam preparation. Students can use them to revise chemical equations, reaction types, balancing methods, important examples, NCERT activities, and frequently asked questions from CBSE Class 10 Science Notes.
| Topic | What You Will Learn |
| Chemical Reaction | How substances change into new substances |
| Chemical Equation | How reactions are written using symbols and formulae |
| Balanced Chemical Equation | Why atoms must be equal on both sides |
| Combination Reaction | Two or more substances combine to form one product |
| Decomposition Reaction | One compound breaks into simpler substances |
| Displacement Reaction | A more reactive element displaces a less reactive element |
| Double Displacement Reaction | Exchange of ions between two compounds |
| Precipitation Reaction | Formation of an insoluble solid |
| Oxidation and Reduction | Gain/loss of oxygen or hydrogen |
| Corrosion | Slow damage of metals due to chemical reaction |
| Rancidity | Spoilage of fats and oils due to oxidation |
Students can download the Chemical Reactions and Equations Class 10 Notes PDF for quick revision before school exams, pre-boards, and CBSE board exams. The PDF includes important definitions, balanced chemical equations, types of chemical reactions, redox reactions, corrosion, rancidity, and NCERT-based examples from Class 10 Science Chapter 1.
A chemical reaction is a process in which one or more substances change to form new substances with different properties. The substances that take part in a reaction are called reactants, and the new substances formed are called products.
Reactants → Products
Magnesium + Oxygen → Magnesium oxide
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When magnesium ribbon burns in oxygen, it forms magnesium oxide and gives a bright white flame.
Balanced equation:
2Mg + O₂ → 2MgO
A chemical reaction may be identified by one or more of the following changes:
| Observation | Example |
| Change in state | Gas formation during a reaction |
| Change in colour | Blue copper sulphate solution turns green when iron is added |
| Evolution of gas | Zinc reacts with dilute acid to produce hydrogen gas |
| Change in temperature | Heat is released or absorbed |
| Formation of precipitate | Barium sulphate forms as a white precipitate |
| Formation of new substance | Burning of magnesium forms magnesium oxide |
A chemical equation is a short way of representing a chemical reaction using symbols and chemical formulae. It shows the reactants on the left-hand side and products on the right-hand side.
Magnesium + Oxygen → Magnesium oxide
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Mg + O₂ → MgO
This equation is called a skeletal chemical equation because it is not balanced.
A skeletal chemical equation represents a reaction using chemical formulae, but the number of atoms of each element may not be equal on both sides.
Example:
Mg + O₂ → MgO
Here, oxygen atoms are not balanced because there are 2 oxygen atoms on the reactant side and only 1 oxygen atom on the product side.
Balanced equation:
2Mg + O₂ → 2MgO
A balanced chemical equation has the same number of atoms of each element on the reactant and product sides. It follows the Law of Conservation of Mass, which states that mass can neither be created nor destroyed in a chemical reaction.
Unbalanced equation:
Fe + H₂O → Fe₃O₄ + H₂
Balanced equation:
3Fe + 4H₂O → Fe₃O₄ + 4H₂
In the balanced equation, the number of iron, hydrogen, and oxygen atoms is equal on both sides.
Balancing a chemical equation is necessary because atoms are neither created nor destroyed in a chemical reaction. Only their arrangement changes. Therefore, the number of atoms of each element must remain the same before and after the reaction.
A balanced equation helps students understand:
Let us balance this equation:
Fe + H₂O → Fe₃O₄ + H₂
| Element | Reactant Side | Product Side |
| Fe | 1 | 3 |
| H | 2 | 2 |
| O | 1 | 4 |
Fe₃O₄ has 3 iron atoms, so place 3 before Fe.
3Fe + H₂O → Fe₃O₄ + H₂
Fe₃O₄ has 4 oxygen atoms, so place 4 before H₂O.
3Fe + 4H₂O → Fe₃O₄ + H₂
Now the reactant side has 8 hydrogen atoms, so place 4 before H₂.
3Fe + 4H₂O → Fe₃O₄ + 4H₂
3Fe + 4H₂O → Fe₃O₄ + 4H₂
| Symbol | Meaning |
| (s) | Solid |
| (l) | Liquid |
| (g) | Gas |
| (aq) | Aqueous solution |
| Δ | Heat |
| ↑ | Gas evolved |
| ↓ | Precipitate formed |
| → | Gives / produces |
| ⇌ | Reversible reaction |
CaO(s) + H₂O(l) → Ca(OH)₂(aq) + Heat
This reaction shows that quicklime reacts with water to form slaked lime and releases heat.
Class 10 Science Chapter 1 includes the following major types of chemical reactions:
A combination reaction is a chemical reaction in which two or more reactants combine to form a single product.
A + B → AB
CaO + H₂O → Ca(OH)₂ + Heat
Quicklime reacts with water to form slaked lime. This reaction releases heat, so it is also an exothermic reaction.
C + O₂ → CO₂
Carbon combines with oxygen to form carbon dioxide.
2H₂ + O₂ → 2H₂O
Hydrogen and oxygen combine to form water.
A decomposition reaction is a chemical reaction in which a single compound breaks down into two or more simpler substances.
AB → A + B
Decomposition reactions usually require energy in the form of heat, electricity, or light.
A thermal decomposition reaction takes place when heat is used to break a compound into simpler substances.
CaCO₃ → CaO + CO₂
Calcium carbonate decomposes on heating to form calcium oxide and carbon dioxide.
2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
Ferrous sulphate crystals decompose on heating and form ferric oxide, sulphur dioxide, and sulphur trioxide.
An electrolytic decomposition reaction takes place when electricity is passed through a compound to break it into simpler substances.
2H₂O → 2H₂ + O₂
Water decomposes into hydrogen and oxygen when electric current is passed through it.
A photochemical decomposition reaction takes place when light is used to break a compound.
2AgCl → 2Ag + Cl₂
Silver chloride decomposes in sunlight to form silver and chlorine.
2AgBr → 2Ag + Br₂
This reaction is used in black-and-white photography.
| Basis | Combination Reaction | Decomposition Reaction |
| Meaning | Two or more substances form one product | One compound breaks into simpler substances |
| General form | A + B → AB | AB → A + B |
| Energy | May release energy | Usually requires energy |
| Example | CaO + H₂O → Ca(OH)₂ | CaCO₃ → CaO + CO₂ |
A displacement reaction is a reaction in which a more reactive element displaces a less reactive element from its compound.
A + BC → AC + B
Fe + CuSO₄ → FeSO₄ + Cu
When an iron nail is dipped in copper sulphate solution, iron displaces copper because iron is more reactive than copper. The blue colour of copper sulphate solution changes to green due to the formation of iron sulphate.
Zn + CuSO₄ → ZnSO₄ + Cu
Zinc is more reactive than copper, so it displaces copper from copper sulphate solution.
A double displacement reaction is a reaction in which two compounds exchange ions to form two new compounds.
AB + CD → AD + CB
Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl
Sodium sulphate reacts with barium chloride to form barium sulphate and sodium chloride. Barium sulphate is an insoluble white precipitate.
A precipitation reaction is a type of double displacement reaction in which an insoluble solid is formed. This insoluble solid is called a precipitate.
Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl
Here, BaSO₄ is the white precipitate.
Pb(NO₃)₂ + 2KI → PbI₂↓ + 2KNO₃
Lead iodide is formed as a yellow precipitate.
| Basis | Displacement Reaction | Double Displacement Reaction |
| Meaning | One element displaces another from a compound | Two compounds exchange ions |
| Reactants | Element + compound | Compound + compound |
| Product | New element and new compound | Two new compounds |
| Example | Fe + CuSO₄ → FeSO₄ + Cu | Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl |
An exothermic reaction is a chemical reaction in which heat is released.
Reactants → Products + Heat
CaO + H₂O → Ca(OH)₂ + Heat
CH₄ + 2O₂ → CO₂ + 2H₂O + Heat
Respiration is also an exothermic process because energy is released when glucose breaks down in the presence of oxygen.
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy
An endothermic reaction is a chemical reaction in which heat is absorbed.
Reactants + Heat → Products
CaCO₃ + Heat → CaO + CO₂
Decomposition of calcium carbonate requires heat, so it is an endothermic process.
| Basis | Exothermic Reaction | Endothermic Reaction |
| Heat change | Releases heat | Absorbs heat |
| Temperature effect | Surroundings become warmer | Surroundings become cooler |
| Example | Respiration | Thermal decomposition |
| General form | Reactants → Products + Heat | Reactants + Heat → Products |
Oxidation and reduction are important parts of Class 10 Science Chapter 1. These reactions are often studied together as redox reactions.
Oxidation is:
Reduction is:
A redox reaction is a reaction in which oxidation and reduction happen at the same time.
CuO + H₂ → Cu + H₂O
In this reaction:
So, this is a redox reaction.
| Term | Meaning |
| Oxidising agent | Substance that gives oxygen or removes hydrogen |
| Reducing agent | Substance that removes oxygen or gives hydrogen |
In the reaction:
CuO + H₂ → Cu + H₂O
Corrosion is the slow eating away of metals due to reaction with air, moisture, acids, or other substances around them.
Rusting is the corrosion of iron. Iron reacts with oxygen and moisture to form hydrated iron oxide, commonly called rust.
4Fe + 3O₂ + xH₂O → 2Fe₂O₃·xH₂O
Rancidity is the oxidation of fats and oils present in food. It causes unpleasant smell, bad taste, and spoilage of food items.
| Basis | Corrosion | Rancidity |
| Meaning | Damage of metals due to chemical reaction | Spoilage of fats and oils due to oxidation |
| Affected substance | Metals | Food containing fats and oils |
| Example | Rusting of iron | Stale chips |
| Prevention | Painting, oiling, galvanisation | Antioxidants, airtight packing, nitrogen flushing |
| Reaction | Balanced Equation |
| Burning of magnesium | 2Mg + O₂ → 2MgO |
| Quicklime with water | CaO + H₂O → Ca(OH)₂ + Heat |
| Burning of coal | C + O₂ → CO₂ |
| Formation of water | 2H₂ + O₂ → 2H₂O |
| Decomposition of calcium carbonate | CaCO₃ → CaO + CO₂ |
| Decomposition of ferrous sulphate | 2FeSO₄ → Fe₂O₃ + SO₂ + SO₃ |
| Electrolysis of water | 2H₂O → 2H₂ + O₂ |
| Decomposition of silver chloride | 2AgCl → 2Ag + Cl₂ |
| Iron with copper sulphate | Fe + CuSO₄ → FeSO₄ + Cu |
| Zinc with copper sulphate | Zn + CuSO₄ → ZnSO₄ + Cu |
| Sodium sulphate with barium chloride | Na₂SO₄ + BaCl₂ → BaSO₄ + 2NaCl |
| Lead nitrate with potassium iodide | Pb(NO₃)₂ + 2KI → PbI₂ + 2KNO₃ |
| Respiration | C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy |
Magnesium ribbon is cleaned and then burned in air. It burns with a bright white flame and forms white magnesium oxide.
Equation:
2Mg + O₂ → 2MgO
Quicklime reacts with water to form slaked lime and releases heat. This is a combination reaction and also an exothermic reaction.
Equation:
CaO + H₂O → Ca(OH)₂ + Heat
Ferrous sulphate crystals decompose on heating and form ferric oxide, sulphur dioxide, and sulphur trioxide. This is a thermal decomposition reaction.
Equation:
2FeSO₄ → Fe₂O₃ + SO₂ + SO₃
When iron nails are kept in copper sulphate solution, the blue colour changes to green because iron displaces copper from copper sulphate solution.
Equation:
Fe + CuSO₄ → FeSO₄ + Cu
When sodium sulphate solution reacts with barium chloride solution, a white precipitate of barium sulphate is formed.
Equation:
Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl
| Mistake | Correct Approach |
| Changing formulae while balancing equations | Only change coefficients, never change formulae |
| Confusing displacement and double displacement reactions | Check whether reactants are element + compound or compound + compound |
| Writing oxidation as only oxygen gain | Also remember loss of hydrogen |
| Forgetting state symbols | Use (s), (l), (g), and (aq) where required |
| Ignoring precipitate symbol | Use ↓ when an insoluble solid forms |
| Mixing corrosion and rancidity | Corrosion is for metals, rancidity is for fats and oils |
A student takes blue copper sulphate solution in a beaker and places a clean iron nail in it. After some time, the blue colour of the solution changes to green, and a reddish-brown deposit appears on the iron nail.
Assertion: A chemical equation should be balanced.
Reason: Mass is conserved in a chemical reaction.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: Respiration is an exothermic reaction.
Reason: Energy is released during the breakdown of glucose.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
Assertion: Silver chloride turns grey in sunlight.
Reason: Silver chloride decomposes into silver and chlorine in the presence of sunlight.
Answer: Both Assertion and Reason are true, and Reason is the correct explanation of Assertion.
| Concept | Key Point |
| Chemical reaction | New substances are formed |
| Reactants | Substances that take part in a reaction |
| Products | Substances formed after reaction |
| Balanced equation | Same atoms on both sides |
| Combination | A + B → AB |
| Decomposition | AB → A + B |
| Displacement | A + BC → AC + B |
| Double displacement | AB + CD → AD + CB |
| Oxidation | Gain of oxygen or loss of hydrogen |
| Reduction | Loss of oxygen or gain of hydrogen |
| Corrosion | Damage of metals |
| Rancidity | Oxidation of fats and oils |
To score well in Chemical Reactions and Equations, students should practise balancing equations, identify reaction types from examples, revise redox concepts carefully, and remember daily-life examples such as rusting, rancidity, respiration, and nitrogen flushing. This chapter becomes easy when equations and examples are revised regularly.
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A magnesium ribbon is cleaned with sandpaper to remove the protective layer of magnesium oxide or basic magnesium carbonate formed on its surface. Once this layer is removed, fresh magnesium reacts easily with oxygen and burns with a dazzling white flame to form magnesium oxide.
A chemical equation must be balanced to follow the Law of Conservation of Mass. This law states that mass is neither created nor destroyed in a chemical reaction. Therefore, the number of atoms of each element must be equal on both reactant and product sides.
In a displacement reaction, a more reactive element displaces a less reactive element from its compound. In a double displacement reaction, two compounds exchange ions to form two new compounds. Displacement involves element and compound, while double displacement involves two compounds.
Respiration is considered an exothermic reaction because glucose breaks down in body cells in the presence of oxygen to produce carbon dioxide, water, and energy. Since energy is released during this process, respiration is classified as an exothermic reaction.
Rancidity is the oxidation of fats and oils in food, which causes unpleasant smell, bad taste, and spoilage. It can be prevented by adding antioxidants, using airtight containers, vacuum packing, refrigeration, and flushing food packets with nitrogen gas.
A balanced chemical equation has the same number of atoms of each element on both sides of the equation. It represents a chemical reaction correctly and follows the Law of Conservation of Mass, which states that mass remains conserved during a reaction.
The main types of chemical reactions in Class 10 are combination, decomposition, displacement, double displacement, precipitation, oxidation-reduction, exothermic, and endothermic reactions. Students should revise definitions, examples, and balanced equations for each type.
Copper sulphate solution changes from blue to green because iron displaces copper from copper sulphate solution. Iron forms iron sulphate, which is green in colour, and copper gets deposited on the iron nail as a reddish-brown layer.