Class 10th || Science || Notes || Chapter 1: Chemical Reactions and Equations

Chapter 1: Chemical Reactions and Equations

  1. Introduction to Chemical Reactions

-        Chemical Reaction: A process in which one or more substances (reactants) are converted into one or more different substances (products).

-        Examples: Rusting of iron, burning of wood, digestion of food.

 

 2. Characteristics of Chemical Reactions

-        Change in State: Formation of a gas, liquid, or solid.

-        Change in Color: Example: Copper sulfate solution changes from blue to green when iron is added.

-        Evolution of Gas: Example: Reaction between zinc and hydrochloric acid produces hydrogen gas.

-        Change in Temperature: Exothermic reactions release heat, while endothermic reactions absorb heat.

-        Formation of Precipitate: A solid formed in a solution during a chemical reaction.

 

 3. Chemical Equations

-        Definition: A representation of a chemical reaction using symbols and formulas.

-        Parts of a Chemical Equation:

-        Reactants: Substances that undergo the chemical change.

-        Products: New substances formed as a result of the reaction.

-        Example: 2H₂ + O₂ à 2H₂O

 4. Balancing Chemical Equations

-        Law of Conservation of Mass: Mass is neither created nor destroyed in a chemical reaction. Therefore, the number of atoms of each element must be the same on both sides of the equation.

-        Steps to Balance:

1.     Write the unbalanced equation.

2.     Count the number of atoms of each element on both sides.

3.     Use coefficients to balance the atoms, starting with the most complex molecule.

4.     Check to ensure all atoms are balanced.

 

 5. Types of Chemical Reactions

-        Combination Reaction: Two or more substances combine to form a single product.

-        Example: CaO + H₂O à Ca(OH)₂

-        Decomposition Reaction: A single compound breaks down into two or more simpler substances.

-        Example: 2H₂O à2H₂ + O₂

-        Displacement Reaction: One element displaces another element in a compound.

-        Example: CuSO₄ + Fe à Cu + FeSO₄

-        Double Displacement Reaction: Exchange of ions between two compounds.

-        Example: Na₂SO₄ + BaCl₂ à 2NaCl + BaSO₄

-        Redox Reactions: Reactions involving oxidation (loss of electrons) and reduction (gain of electrons).

-        Example: Zn + CuSO₄ à Cu + ZnSO₄ (Zn is oxidized, Cu is reduced)

 

 6. Effects of Oxidation Reactions in Everyday Life

-        Corrosion: The gradual destruction of metals by chemical reactions with the environment (e.g., rusting of iron).

-        Rancidity: The oxidation of fats and oils in food, leading to a bad taste and smell.

 

 7. Prevention of Corrosion and Rancidity

-        Corrosion:

-        Painting, Greasing, and Galvanization: Coating metal surfaces to prevent exposure to moisture and air.

-        Alloying: Mixing metals with other elements to improve corrosion resistance.

-        Rancidity:

-        Antioxidants: Adding substances that prevent oxidation of fats and oils.

-        Refrigeration: Slowing down the rate of oxidation by storing food at low temperatures.

 

 Key Terms

-        Reactant: A substance that takes part in and undergoes change during a reaction.

-        Product: A substance produced during a chemical reaction.

-        Precipitate: An insoluble solid formed from a solution during a chemical reaction.

-        Exothermic Reaction: A reaction that releases energy in the form of heat.

-        Endothermic Reaction: A reaction that absorbs energy in the form of heat.

-        Oxidation: The loss of electrons or an increase in oxidation state by a molecule, atom, or ion.

-        Reduction: The gain of electrons or a decrease in oxidation state by a molecule, atom, or ion.