Short Notes 2-Class 10 – Science -Chemistry -Chapter 1 – Chemical Reaction and Equation

Class 10 – Science -Chemistry -Short Notes 2 -Chapter 1 – Chemical Reaction and Equation

Types of Chemical Reactions:

1.    Combination Reactions:

        Two or more substances combine to form a new substance.

        General form: A + B → AB

        Mg(s) + O2(g) → 2MgO(s)

        Magnesium + Oxygen → Magnesium Oxide

2.    Decomposition Reactions:

       A single substance breaks down into two or more simpler substances.

       General form: AB → A + B

       C (s) + O2(g) → CO2(g)

        Carbon + Oxygen → Carbon dioxide

3.    Displacement Reactions:

       One element displaces another element from its compound.

       Single displacement: A + BC → AC + B

       Double displacement: AB + CD → AD + BC

4.   Double Displacement Reaction:

       Reactions in which ions are exchanged between two reactants forming new compounds are called Double Displacement Reactions.

       AB + CD → AC + BD

Examples:

               When the solution of barium chloride reacts with the solution of sodium sulphate, white precipitate of barium sulphate is      formed along with sodium chloride.

          BaCl2(aq) + Na2SO4(aq) → BaSO4(s) (Precipitate) + 2NaCl(aq)

           When sodium hydroxide (a base) reacts with hydrochloric acid, sodium chloride and water are formed.

          NaOH(aq) + HCl(aq) → NaCl(aq) + H2O(l)

           Note: Double Displacement Reaction, in which precipitate is formed, is also known as precipitation reaction. Neutralisation reactions are also examples of double displacement reaction.

5.    Redox Reactions:

       Chemical reaction in which both oxidation and reduction take place simultaneously.

• Oxidation: Reaction that involves the gain of oxygen or loss of hydrogen.
•  Reduction: Reaction that shows the loss of oxygen or gain of hydrogen.

              ZnO + C → Zn + CO

              ZnO is reduced to Zn—reduction. C is oxidized to CO—Oxidation.

Effects of Oxidation Reactions in Our Daily Life:

      Corrosion: The gradual eating up of metals by the action of air and moisture on their surface  is called corrosion.

The most common example of corrosion is rusting of iron.

4Fe + 3O₂ + 2nH₂O → 2Fe₂O₃.nH₂O

Steps to prevent rusting of iron:

(i) Coating the iron surface with oil, grease or paint
(ii) Depositing a layer of zinc on the surface of iron. This process is called galvanisation.
(iii) Forming alloys of iron

           Rancidity: When fats and oils are exposed to air, they get oxidized and become rancid and their smell and colour change. This phenomenon is called rancidity

Steps to prevent rancidity:
(i) Storing food materials in air-tight containers
(ii) Packaging food items in bags containing nitrogen
(iii) Refrigeration of food items
(iv) Addition of antioxidants or preservatives to the foods containing fats and oils

Types of Chemical Equations:

1.    Skeleton Equations:

       Initial, unbalanced representation of a chemical reaction.

2.    Balanced Equations:

        Coefficients adjusted to satisfy the law of conservation of mass.

Importance of Chemical Equations:

•        Provide a concise and standardized way to represent chemical reactions.
•       Facilitate the understanding of reaction stoichiometry.
•       Essential for predicting and understanding the outcomes of chemical reactions.

Understanding chemical reactions and equations is fundamental in the study of chemistry, forming the basis for more advanced concepts in later classes.