science class 10

Chemical Reactions and Equations for CBSE 2024-25

Introduction to Chemical Reactions

Importance of Chemical Reactions in Daily Life:

  • Milk left at room temperature (spoiling)

  • Iron exposed to humid conditions (rusting)

  • Fermentation of grapes (making wine)

  • Cooking of food (changes in composition)

  • Digestion of food (breakdown of nutrients)

  • Respiration in living organisms (energy release)

Distinction Between Physical and Chemical Changes

  • Definition: Chemical reactions involve changes in the identity of substances.

Indicators of Chemical Reactions

Key Observations that Indicate a Chemical Reaction:

  • Change in State (solid, liquid, gas)

  • Change in Color

  • Evolution of Gas

  • Change in Temperature

Activity Examples:

  • Burning magnesium ribbon to form magnesium oxide.

  • Reaction of zinc granules with dilute acid to produce hydrogen gas.

Writing Chemical Equations

Word Equations

  • Example: Reaction of magnesium and oxygen:

    • Magnesium + Oxygen → Magnesium Oxide

  • Reactants are substances that undergo chemical change.

  • Products are the new substances formed.

Chemical Equations

  • Word equations can be simplified using chemical formulas:

    • From word equation: Mg + O2 → MgO

Importance of Balancing Chemical Equations

  • Law of Conservation of Mass:

    • Balanced equations have equal number of each type of atom on both sides.

Writing and Balancing Equations

Steps to Balance a Skeletal Equation:

  1. Write down the unbalanced equation.

  2. Count atoms of each element on both sides.

  3. Adjust coefficients to balance each element.

  4. Check if both sides have equal number of each atom.

Types of Chemical Reactions

Combination Reactions

  • Definition: Two or more reactants combine to form a single product.

  • Example: Formation of slaked lime (calcium hydroxide) from calcium oxide and water.

Decomposition Reactions

  • Definition: Breakdown of a single substance into two or more simpler products.

  • Example: Heating lead nitrate to produce lead oxide, nitrogen dioxide, and oxygen.

Displacement Reactions

  • Definition: An element or ion in a compound is replaced by another element or ion.

  • Example: Zinc displacing copper from copper sulfate solution.

Double Displacement Reactions

  • Definition: Exchange of ions between two compounds leading to the formation of two new compounds.

  • Example: Precipitation reactions like: Barium Chloride + Sodium Sulfate → Barium Sulfate (precipitate) + Sodium Chloride.

Oxidation and Reduction

Reaction Characteristics:

  • Oxidation: Gain of oxygen or loss of hydrogen by a substance.

  • Reduction: Loss of oxygen or gain of hydrogen.

  • Example: Rusting of iron involves oxidation.

Practical Applications of Chemical Reactions

  • Chemical equations and reactions are integral in industries and laboratories for the synthesis of products, waste treatment, etc.

Summary of Key Concepts

  • Understanding chemical reactions involves recognizing change in physical and chemical properties, writing balanced equations, and categorizing reactions.

  • Real-world applications highlight the fundamental role chemical reactions play in everyday processes and industries.

Common Reactions

  1. Combustion Reaction: Hydrocarbon + Oxygen → Carbon Dioxide + Water

    • Example: CH4 + 2O2 → CO2 + 2H2O.

  2. Neutralization Reaction: Acid + Base → Salt + Water

    • Example: HCl + NaOH → NaCl + H2O.

  3. Single Replacement Reaction: A + BC → AC + B

    • Example: Zn + CuSO4 → ZnSO4 + Cu.

  4. Decomposition of Hydrogen Peroxide: 2H2O2 → 2H2O + O2 (using a catalyst).