Syllabus and Basic concepts of CBSE Class 10th (chemical reactions and equations).

Syllabus of chapter 1 Chemical reactions and equations

1. chemical equations:

                 (i) writing a chemical equation 

                   (ii) Balanced chemical equations

                  (iii) implications of balanced

                                   Chemical equations.

 

2. Types of chemical reactions:

                 (i) Combination reaction

                   (ii) Decomposition reaction

                  (iii) Displacement reaction

                  (iv) Double Displacement reaction

                   (v) Endothermic reaction

                  (vi) Exothermic reaction

                 (vii) Precipitation reaction

                (viii) Neutralization reaction

                  (ix) Oxidation reaction

                   (x)  Reduction reaction

                   (xi) Redox reaction.

    

3. The Effects of Oxidation reactions in every day life:

                 (i) Corrosion

                 (ii) Rancidity.

Basic concepts of Chemical reactions and equations:

1. Chemical reactions taking place are represented by the fully balanced chemical equations,i.e., the number of atoms of each type involved in a reaction are the same on the reactant and product side of the chemical equation.

   Characteristics of chemical reactions:

     - change in State (s, l, g, aq)

     - change in colour

     - Evolution of a gas (∆)

     - change in temperature

     - formation of precipitate.

   Note: state of reactants are written in equation. (aq) is written if the reactant or product is present as a solution in water.

2. A simple equation is balanced by hit and trial method so that same total number of charges and atoms appear on both the sides of the equation. For example when Iron combines with steam to form Fe3O4 and H2, it is balanced in the following steps: 

(i)  Fe + H2O ---› Fe3O4 + H2

(ii) Fe + 4H2O ---› Fe3O4 + H2

(iii) Fe +4H2O---›  Fe3O4+4H2

(iv) 3Fe +4H2O---› Fe3O4 +4H2

     

In the first case the equation is unbalanced. Such equations are called skeletal chemical equation.

Note that we need balance a Chemical equation in order to satisfy law of Conservation of Mass (that mass can neither be created nor be destroyed in a reaction).

So therefore,

In the (ii) step O is made equal on both the sides.

In the (iii) step H is made equal on both the sides.

In the (iv) step Fe is made equal on both the sides.

---› If the reaction is complicated,i.e., it involves large number of reactants and products, it is written in steps which are balanced as above and then added up to get the final reactants and products. This is called partial equation method.

3. A complete chemical equation gives the formulae of the reactants and products, their physical states(s, l, g, aq) and brief conditions under which a reaction occurs.(Catalyst used, temperature etc are written above or below the arrow).

4.there are several types of reactions. These involve breaking of bonds and formation of new ones by the effect of heat, light or Mechanical shaking.

      (i) In Combination reaction, two or more Substances (Elements or Compounds) combine to form a new substance (as product).

E.g., Magnesium ribbon burns with dazzling white light to form Magnesium Oxide.

     2Mg + O2 ---›  2MgO

      (ii) A Decomposition reaction occurs when a compound is broken into smaller parts. It may be either Thermal Decomposition(in presence of heat) or Electrolytic Decomposition(in presence of electricity) or photochemical decomposition (in presence of light).

E.g., Thermal- 2FeSO4(s)----›

                          Fe2O3(s)+SO2(g)+ SO3(g)

         Electrolytic- 2H2O ---›2H2 + O2

         Photochemical- 2Agcl ---› 2Ag+ Cl2

    

      (iii) The reaction in which an atom or group of atoms in a molecule is replaced by another atom or group of atoms is called Displacement reaction.

E.g., Ferrous(iron) reacts with cupper sulphate solution to form Ferrous sulphate and cupper.

 Fe(s) + CuSO4(aq) ---› FeSO4(aq) + Cu(s)

      (iv) when two reacting molecules exchange their partner ions in solution, it will be Double Displacement reaction.

{Note : when a substance breaks up into its ions then it's said to be dissociation reaction}.

E.g., Na2SO4 + BaCl2 ---›BaSO4 + 2NaCl 

      (v) Reactions in which energy is absorbed are known as Endothermic chemical reactions.

E.g., CaCO3 + heat ---› CaO + CO2

     (vi) Reactions in which energy is released in the form of heat, along with the formation of products are called Exothermic chemical reactions.

E.g., CaO + H2O ---› Ca(OH)2 + heat

     (vii) In Precipitation reaction, Insoluble salts are formed.

E.g., Na2SO4+BaCl2 ---›BaSO4(s)+2NaCl

     Here BasO4 is precipitate. Precipitate are insoluble so they are represented as (s).

     (viii) Neutralization reaction is a reaction in which Acid and base react to form salt and water.

E.g., HCl(aq)+NaOH(aq)---›NaCl(s)+ H2O

      (ix) Oxidation reaction is a reaction in which oxygen/any electronegative element is added up OR Hydrogen/any electropositive element is removed.

E.g., 2Cu + O2 ---› CuO {cu is oxidised}

       (x) Reduction reaction is a reaction in which Hydrogen/any electropositive element is added up OR Oxygen/any electronegative element is removed.

E.g., Cl2(g) + H2(g) ---›2HCl(g)

 

      (xi) In some reactions, one reactant gets oxidised while the other gets reduced during a reaction,such reaction are called Oxidation-Reduction reactions or Redox Reactions.

E.g., CuO + H2 ---› Cu + H2O

Effects of Oxidation reactions in everyday life:

        (i) Corrosion: Due to the effects of Moisture and Acids, Metals get corroded. This effect is called Corrosion.

    Corrosion causes damage to Iron railing, Bridges, Car bodies etc.

     Rusting of Iron is the biggest issue causes by Corrosion.It can be prevented by painting, oiling, greasing, galvanizing, chrome plating, anodising or making of alloys.

        (ii) Rancidity: Fats and oils in food kept for long time get oxidised and become rancid and taste of food changes and causes infection on eating, this is called rancidity.

                    In order to prevent the food from Rancidity;

              - Antioxidants are added,

              - storing food in air tight 

                  Containers.

              - keeping fruits and 

                  Vegetables in fridge

              - Even snacks packs are

                   Filled with Nitrogen to 

                   Prevent from Rancidity.