NOTES -CH-1-CHEMICAL REACTION AND EQUATION || NCERT Notes For Class 10 Science Chapter 1 Chemical Reactions And Equations

NOTES - CH-1-CHEMICAL REACTION AND EQUATION

NCERT Notes For Class 10 Science Chapter 1 Chemical Reactions And Equations.

Class 10 Science Chapter 1 Chemical Reactions And Equations Notes.
Chemical Reactions and Equations – Class 10 Science Notes.

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CHEMICAL REACTION EQUATION

Chemical reaction is the process in which new substances with new properties are formed from one or more substances is called Chemical Reaction.

During chemical reaction following changes has taken place:-

(i) Change in state     (ii) Change in colour

(iii) Evolution of gas  (iv)Change in temperature

Reactants :- The substance which take part in chemical reactions are called Reactants.

Reactant --- on the left-hand side

Products :- The substance which are formed in a chemical reaction are Called Products.

Product --- on the right-hand side.

Ways of Representing a chemical Reaction :-

Chemical Equation :- A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formula.

According to LAW OF CONSERVATION OF MASS Number of elements  in a Chemical reaction should remain same at Reactant and Product Side.

Balanced chemical equation:-

In a Balanced chemical equation :- the number of atoms of different elements on both side of the equation (Reactant and Product side)  is always equal.

Eg. :-

Aqueous (aq) is written if the reactant or product is present as a solution in water.

TYPES OF CHEMICAL REACTIONS:-

1)COMBINATION REACTION:-  The reaction in which two or more reactants combine to form a single product.

OR

It is a reaction in which a single product is formed from two or more reactants is known as a combination reaction.

 e.g. :-

Slaked lime is used for white washing walls.

Calcium hydroxide reacts slowly with the carbon dioxide in air to form a thin layer of calcium carbonate on the walls.

Calcium carbonate is formed after two to three days of white washing and gives a shiny finish to the walls.

Exothermic Reactions:- Reaction in which heat is released along with formation of products.

e.g. :-

DECOMPOSITION REACTION:- The reaction in which a single compound splits into two or more simple substances is called decomposition reaction.

A  →   B+C

Thermal decomposition:-When decomposition is carried out by heating.

e.g.,

                                           

Electrolytic  Decomposition:- When decomposition is carried out by passing electricity.

Photolytic Decomposition:- When decomposition is carried out in presence of sunlight.

Eg.,

Endothermic Reactions :- The reactions which require energy in the form of heat or light  to break reactants are called endothermic reactions.

Eg.,

DISPLACEMENT REACTION :- The chemical reaction in which more reactive element displaces less reactive element from its salt solution.

Iron is more reactive element than copper. They displace copper from its compounds.

#  OXIDATION AND REDUCTION :-

Oxidation:-

(i) The addition of oxygen to substance OR

(ii) The removal of hydrogen from a substance.

(Cu is Oxidized to CuO)

If a substance gains oxygen during a reaction, it is said to be oxidized.

The Substance  which either gives Oxygen or removes hydrogen in an oxidation reaction is known as oxidizing agent. 

Reduction :-

(i) The addition of hydrogen to substance OR

(ii) The removal of Oxygen from a substance.

Reduction (CuO is reduced to Cu)

Redox reaction:- A reaction in which  oxidation and reduction taking place together is called a redox reaction.

 Hydrogen ( H2) is a reducing agent as it undergo Oxidation.

CuO is an Oxidising agent as undergo reduction.

 

In this reaction CuO is reduced to Cu and H2 is oxidized to H2O.

Carbon ( C) is a reducing agent as it undergo Oxidation.

ZnO is an Oxidising agent as undergo reduction.

 

In this reaction ZnO is reduced to Zn and C is oxidized to CO.

HCl is a reducing agent as it undergo Oxidation.

MnO2 is an Oxidising agent as undergo reduction.

In this reaction MnO2 is reduced to MnCl2 and HCl is oxidized to Cl2.

3CO is a reducing agent as it undergoes Oxidation.

Fe2O3 is an Oxidising agent as undergoes reduction.

In this reaction Fe2O3 is reduced to 2Fe and 3CO is oxidized to 3CO2.

Oxidizing agent:-

• The substance which gives oxygen for oxidation or removes, hydrogen is called an Oxidizing agent

Reducing agent:-

• The substance which gives hydrogen or removes oxygen for reduction is called a Reducing agent. 

Effects of Oxidation Reaction in Daily Life :-

1) Corrosion :- The Process of Slow and gradual Conversion of metals into their undesirable compounds due to their reaction with air, moisture(water) present in the atmosphere is called Corrosion.

Eg:- Rusting of Iron

Rusting:- Iron when reacts with oxygen and moisture forms the red substance which is called Rust.

4Fe(s) + 30₂(g) + H₂0 (l) — 2Fe₂O₃. xH₂0 (s)

Hydrated Ferric oxide (Rust)

The rusting of iron is a redox reaction.

Corrosion (rusting) weakens the iron and steel objects and structures such as railings, car bodies, bridges and ships etc. and cuts short their life.

 Methods to Prevent Rusting:-
• By painting.              
• greasing and oiling. 
• galvanization                 
• electroplating

Corrosion of Copper: Copper objects lose their lustre and shine after some time because the surface of these objects acquires a green coating of basic copper carbonate  Cuco₃.Cu(OH) ₂  when exposed to air.

Corrosion of Silver Metal:- The surface of silver metal  becomes dull on exposure to air, due to the formation of a coating of black silver sulphide (Ag_2 S) on its surface by the action of H2S gas present in the air.

Rancidity:- The oxidation of fats and oils when exposed to air is known as rancidity. It leads to bad smell and bad taste of food.

Rancidity spoils the food materials prepared in fats and oils which have been kept for considerable time and makes them unfit for eating.

Methods to prevent rancidity:-

(i) By adding antioxidants 

(ii) Keeping food in airtight containers
(iii) Replacing air by nitrogen 

(iv) Refrigerator

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