Class 10 Chemistry — Chemical Reactions and Equations FULL MASTER NOTES
CBSE Board 2026 | NCERT Based | Detailed Notes + PYQs + Tricks + Diagrams + Expected Questions
📖 INTRODUCTION
In our daily life, many changes take place around us. Some changes are physical changes while others are chemical changes.
A chemical reaction is a process in which one or more substances react to form new substances with different properties.
🌟 Examples of Chemical Reactions
- Burning of magnesium ribbon
- Rusting of iron
- Digestion of food
- Respiration
- Cooking food
CHARACTERISTICS OF CHEMICAL REACTIONS
The following observations indicate that a chemical reaction has taken place:
- Change in state
- Change in colour
- Evolution of gas
- Change in temperature
- Formation of precipitate
CHEMICAL EQUATION
A symbolic representation of a chemical reaction using symbols and chemical formulas is called a chemical equation.
🌟Example
Word Equation:
Magnesium + Oxygen → Magnesium oxide
Chemical Equation:
2Mg + O_2➔2MgO
REACTANTS AND PRODUCTS
| Term | Meaning |
|---|---|
| Reactants | Substances taking part in reaction |
| Products | New substances formed |
WORD EQUATION
An equation written using names of substances is called a word equation.
Example
Hydrogen + Oxygen → Water
CHEMICAL EQUATION
An equation written using chemical formulas is called a chemical equation.
Example
2H_2 + O_2➔2H_2O
BALANCED CHEMICAL EQUATION ⭐ VERY IMPORTANT
A chemical equation in which the number of atoms of each element is equal on both sides is called a balanced chemical equation.
LAW OF CONSERVATION OF MASS
Mass can neither be created nor destroyed during a chemical reaction.
Therefore, equations must be balanced.
WHY SHOULD EQUATIONS BE BALANCED?
Because atoms are neither created nor destroyed during a chemical reaction.
STEPS OF BALANCING EQUATIONS
- Write the skeletal equation
- Count atoms of each element
- Balance metals first
- Balance non-metals
- Balance hydrogen and oxygen at the end
- Recheck all atoms
EXAMPLE OF BALANCING
Unbalanced Equation
Fe + H_2O→Fe_3O_4 + H_2
Balanced Equation
3Fe + 4H_2O→Fe_3O_4 + 4H_
TYPES OF CHEMICAL REACTIONS
- Combination reaction
- Decomposition reaction
- Displacement reaction
- Double displacement reaction
- Redox reaction
🧪 1. COMBINATION REACTION
A reaction in which two or more substances combine to form a single product.
General Form
A + B→AB
Examples
Formation of Magnesium Oxide
2Mg + O_2→2MgO
Formation of Slaked Lime
CaO + H_2O→Ca(OH)_2
Characteristics
- Single product formed
- Heat is usually released
Application
Formation of slaked lime used in whitewashing.
🧪 2. DECOMPOSITION REACTION
A reaction in which a single compound breaks into simpler substances.
General Form
AB→A + B
TYPES OF DECOMPOSITION
| Type | Cause |
|---|---|
| Thermal decomposition | Heat |
| Electrolytic decomposition | Electricity |
| Photolytic decomposition | Sunlight |
THERMAL DECOMPOSITION
Decomposition caused by heat.
Example
CaCO_3→CaO + CO_2
(Calcium carbonate → Calcium oxide + Carbon dioxide)
ELECTROLYTIC DECOMPOSITION
Decomposition caused by electricity.
Example
2H_2O→{Electricity}→2H_2 + O_2
PHOTOLYTIC DECOMPOSITION
Decomposition caused by sunlight.
Example
2AgCl→{Sunlight}→ 2Ag + Cl_2
IMPORTANT → POINT ⭐
Silver chloride turns grey in sunlight due to the formation of silver metal.
🧪 3. DISPLACEMENT REACTION
A more reactive element displaces a less reactive element from its compound.
General Form
A + BC→aAC + B
Example
Zn + CuSO_4→ZnSO_4 + Cu
Observation
- Blue colour of copper sulphate fades
- Brown copper metal is deposited
🧪 4. DOUBLE DISPLACEMENT REACTION
A reaction in which two compounds exchange ions.
General Form
AB + CD→AD + CB
Example
BaCl_2 + Na_2SO_4→BaSO_4 + 2NaCl
PRECIPITATION REACTION
A reaction that produces an insoluble solid called precipitate.
Observation
White precipitate of barium sulphate is formed.
🧪 5. REDOX REACTION ⭐ VERY IMPORTANT
A reaction involving oxidation and reduction simultaneously.
OXIDATION
- Addition of oxygen
- Removal of hydrogen
Example
2Cu + O_2→2CuO
Copper gets oxidized.
REDUCTION
- Removal of oxygen
- Addition of hydrogen
Example
CuO + H_2→Cu + H_2O
Copper oxide gets reduced.EXAMPLE OF REDOX REACTION
CuO + H_2O→Cu + H_2O
- CuO loses oxygen → Reduction
- H₂ gains oxygen → Oxidation
Thus, oxidation and reduction occur together.
OXIDIZING AGENT
A substance that causes oxidation.
Example:
CuO acts as oxidizing agent.
🌟 REDUCING AGENT
A substance that causes reduction.
Example:
Hydrogen acts as reducing agent.
🌟 EFFECTS OF OXIDATION IN DAILY LIFE
- Corrosion
- Rancidity
🌟 CORROSION ⭐ BOARD IMPORTANT
The slow eating away of metals due to reaction with air and moisture is called corrosion.
🌟 Examples of Corrosion
Rusting of Iron
4Fe + 3O_2 + xH_2O→2Fe_2O_3 \cdot xH_2O
Black coating on silver
Ag + H_2S→Ag_2S
Green coating on copper
2Cu + H_2O + CO_2 + O_2→Cu(OH)_2 + CuCO_3
🌟 PREVENTION OF CORROSION
- Painting
- Greasing
- Galvanization
- Alloying
🌟 RANCIDITY
Oxidation of oils and fats causing bad smell and taste is called rancidity.
🌟 PREVENTION OF RANCIDITY
- Airtight containers
- Refrigeration
- Use of antioxidants
- Nitrogen flushing
🔥 IMPORTANT DIFFERENCES
Combination vs Decomposition Reaction
| Combination Reaction | Decomposition Reaction |
|---|---|
| Single product formed | Single reactant breaks |
| Heat released | Heat often required |
Oxidation vs Reduction
| Oxidation | Reduction |
|---|---|
| Addition of oxygen | Removal of oxygen |
| Removal of hydrogen | Addition of hydrogen |
Displacement vs Double Displacement
| Displacement | Double Displacement |
|---|---|
| One element displaced | Exchange of ions |
| Reactivity series involved | No reactivity series involved |
✍️ IMPORTANT DIAGRAMS & ACTIVITIES
1. Burning Magnesium Ribbon
Observation:
- Bright white flame
- White ash of magnesium oxide formed
2. Electrolysis of Water
Observation:
- Hydrogen gas at cathode
- Oxygen gas at anode
Ratio: Hydrogen : Oxygen = 2 : 1
3. Displacement Reaction Setup
Zn + CuSO_4 \rightarrow ZnSO_4 + Cu
Observation:
- Blue solution becomes colourless
- Copper deposits on zinc strip
4. Rusting of Iron
Conditions needed:
- Air
- Moisture
🧠 SUPER TRICKS
🌟 OIL RIG
- Oxidation Is Loss
- Reduction Is Gain
🌟 Reaction Types Trick
“CDDDR”
- C → Combination
- D → Decomposition
- D → Displacement
- D → Double displacement
- R → Redox
🎯 MOST IMPORTANT BOARD QUESTIONS WITH ANSWERS
Q1. What is a balanced chemical equation?
Answer:
A chemical equation in which the number of atoms of each element is equal on both sides is called a balanced chemical equation.
Q2. What is decomposition reaction? Give one example.
Answer:
A reaction in which a single compound breaks into simpler substances is called decomposition reaction.
Example:
CaCO_3→{\Delta} CaO + CO_2
Q3. What is corrosion? How can it be prevented?
Answer:
Corrosion is the slow damage of metals due to reaction with air and moisture.
Prevention methods:
- Painting
- Greasing
- Galvanization
- Alloying
Q4. Define oxidation and reduction.
Answer:
Oxidation is addition of oxygen or removal of hydrogen.
Reduction is removal of oxygen or addition of hydrogen.
Q5. Why are silver chloride containers kept in dark bottles?
Answer:
Silver chloride decomposes in sunlight and forms silver metal. Therefore, it is stored in dark bottles.
🔥 IMPORTANT NCERT POINTS
- Chemical reactions involve breaking and making of bonds.
- Chemical equations must be balanced.
- Corrosion damages metals.
- Oxidation and reduction occur together.
- Rancidity spoils food materials.
🎯 EXPECTED QUESTIONS FOR CBSE BOARD 2026
- Explain different types of chemical reactions with examples.
- What is corrosion? Explain methods to prevent it.
- Balance the given chemical equations.
- Explain redox reaction with examples.
- Differentiate between oxidation and reduction.
- Explain decomposition reactions.
- What is rancidity? How can it be prevented?
- Why should chemical equations be balanced?
- What is precipitation reaction?
- Explain displacement reaction with example.
⭐ BALANCING CHEMICAL EQUATIONS PRACTICE
(LOW TO HIGH LEVEL QUESTIONS)
🟢 EASY LEVEL
Balanced:
1.2H_2 + O_2→2H_2
2.Mg + O_2 = MgO
Balanced:
2Mg + O_2 = 2MgO
- Fe + S→FeS
Balanced:
Fe + S =FeS
- Na + Cl_2→NaCl
Balanced:
2Na + Cl_2 = 2NaCl
- Ca + O_2→CaO
Balanced:
2Ca + O_2=2CaO
🟡 MEDIUM LEVEL
Al + O_2→Al_2O_3
Balanced:
4Al + 3O_2 2Al_2O_3
Fe + H_2O→Fe_3O_4 + H_2
Balanced:
3Fe + 4H_2O = Fe_3O_4 + 4H_2
NaOH + H_2SO_4→Na_2SO_4 + H_2O
Balanced:
2NaOH + H_2SO_4=Na_2SO_4 + 2H_2O
CaCO_3→CaO + CO_2
Balanced:
CaCO_3 =CaO + CO_2
Zn + HCl→ZnCl_2 + H_2
Balanced:
Zn + 2HCl =ZnCl_2 + H_2
🔴 HIGH LEVEL
- KClO_3→KCl + O_2
Balanced:
2KClO_3 =2KCl + 3O_2
- Pb(NO_3)_2→PbO + NO_2 + O_2
Balanced:
2Pb(NO_3)_2 =2PbO + 4NO_2 + O_2
- C_2H_6 + O_2→CO_2 + H_2O
Balanced:
2C_2H_6 + 7O_2 = 4CO_2 + 6H_2O
- Fe_2O_3 + C→Fe + CO_2
Balanced:
2Fe_2O_3 + 3C =4Fe + 3CO_2
- NH_3 + O_2→NO + H_2O
Balanced:
4NH_3 + 5O_2 = 4NO + 6H_2O
🎯 MOST EXPECTED BOARD PYQs
1. Balance the equation:
MnO_2 + HCl = MnCl_2 + Cl_2 + H_2O
Balanced:
MnO_2 + 4HCl=MnCl_2 + Cl_2 + 2H_2O
2. Identify type of reaction:
AgNO_3 + NaCl =AgCl + NaNO_3
Answer: Double displacement and precipitation reaction.
3. Why is respiration called exothermic reaction?
Answer: Because energy is released during respiration.
4. What happens when iron nails are dipped in copper sulphate solution?
Answer: Iron displaces copper from copper sulphate solution and brown copper gets deposited.
Fe + CuSO_4 =FeSO_4 + Cu
⭐ NCERT ACTIVITIES IMPORTANT FOR BOARD
| Activity | Observation |
|---|---|
| Burning magnesium ribbon | White ash formed |
| Iron nail in CuSO₄ | Brown coating formed |
| Heating ferrous sulphate | Smell of sulphur |
| Electrolysis of water | Hydrogen and oxygen gases formed |
🔥 FINAL REVISION POINTS
- Learn all reaction types with examples
- Practice balancing daily
- Remember definitions exactly
- Focus on NCERT activities
- Learn observations carefully
- Practice PYQs repeatedly
