Ch-1 chemical reaction and equation class 10th notes

 Class 10th Chemistry – Chapter 1: Chemical Reactions and Equations (Deep Conceptual Notes)

1. What is a Chemical Reaction?

A chemical reaction is a process where one or more substances (reactants) are transformed into new substances (products).

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Key features:

Bonds in reactants break.

New bonds form in products.

Energy is either absorbed or released.

Examples:

Rusting of iron: Fe + O₂ + H₂O → Fe₂O₃·xH₂O

Burning of magnesium: 2Mg + O₂ → 2MgO

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2. Chemical Equations

Representation of a chemical reaction using symbols and chemical formulae.

Example: Mg + O₂ → MgO (unbalanced)

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3. Balancing Chemical Equations

Law of Conservation of Mass: Mass is neither created nor destroyed.

Number of atoms of each element must be equal on both sides.

Balanced Example: 2Mg + O₂ → 2MgO

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4. Types of Chemical Reactions

(i) Combination Reaction

Two or more substances combine to form one product.

Example: CaO + H₂O → Ca(OH)₂ (Exothermic)

(ii) Decomposition Reaction

A single compound breaks into two or more simpler substances.

Example: 2H₂O₂ → 2H₂O + O₂

Types: Thermal, Electrolytic, Photolytic

(iii) Displacement Reaction

A more reactive element displaces a less reactive one.

Example: Zn + CuSO₄ → ZnSO₄ + Cu

(iv) Double Displacement Reaction

Ions are exchanged between two compounds.

Example: Na₂SO₄ + BaCl₂ → BaSO₄↓ + 2NaCl

(White precipitate of BaSO₄)

(v) Redox Reaction

Oxidation: Loss of electrons / gain of oxygen

Reduction: Gain of electrons / loss of oxygen

Example: CuO + H₂ → Cu + H₂O

(CuO is reduced, H₂ is oxidized)

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5. Characteristics of a Chemical Reaction

Change in state

Change in color

Evolution of gas

Change in temperature

Formation of precipitate

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6. Corrosion and Rancidity

(i) Corrosion

Metal damage due to air/moisture.

Example: Rusting of iron (Fe → Fe₂O₃·xH₂O)

Prevention: Painting, greasing, galvanization.

(ii) Rancidity

Spoiling of food due to oxidation of fats/oils.

Prevention: Antioxidants, refrigeration, air-tight storage.

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Concept Tips:

Always balance using smallest whole numbers.

Oxidation and reduction happen together (redox pair).

Observe physical changes (color/gas/temp) to identify reactions.

Concept Insights:

Always balance the equation using smallest whole numbers.

Understand oxidation and reduction as opposites happening simultaneously.

Pay attention to color changes, gas evolution, precipitate formation, and temperature change to identify the type of reaction.

Redox reactions are all about electron transfer — one substance gets oxidized, the other gets reduced.

In displacement reactions, check the reactivity series to predict if the reaction will occur.

For decomposition reactions, remember the type of energy required:

Heat → thermal decomposition

Light → photolytic decomposition

Electricity → electrolytic decomposition

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Previous year Questions in this chapter will be coming soon..