CBSE Class 10 Science Revision Notes of Ch.1 Chemical Reactions and Equations 2020

CBSE Class 10 Science Ch.1 Chemical Reactions and Equations Revision Notes 2020  Pdf download

Revision Notes of CBSE Class 10 Science Ch.1 Reactions and Equation

Revision notes of CBSE class 10th Ch.1 Chemical Reactions and Equations is very important from the point of view of board examination.This Chapter of science explains how the world around us is made of. Chemical Reactions are used to explain the various processes that happens around us.
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Chemical Reaction :-  Whenever a chemical change occurs we can say that a chemical reaction has taken place.

A chemical reaction has taken place :-

Change in state        change in colour 

evolution of gas         change in temperature

Chemical equations :-  It is the simplest way to write chemical reaction in the form of word equation

Example :- magnesium(reactants)  + oxygen (reactants) = Magnesium oxide (product)

Reactants :-  The substances that undergo chemical change in the reaction(magnesium and oxygen)  are the reactants

Product :- The new substances(magnesium oxide) formed during the reaction is the product.

 Methods to Write Chemical equation :- 

i) The reactants are written on the left hand side (L.H.S.)  with a plus sign between them.

ii) Products are written on the right hand side with a  plus sign between them.

iii) the arrowhead points is written towards  the product, and shows the direction of the reaction.

Skeletal  chemical equations :- 

Skeletal chemical equation is a representation of a chemical reaction using chemical formulae of reactants and products and it is unbalanced

Balanced Chemical Reaction :-  The number of atoms of each element remains same before and after a chemical reaction. Such reactions are known as Balanced Chemical Reaction.

Balanced Chemical Equation :- The number of atoms of each element is  same on both side of the arrows , is a balanced chemical equation.

Types of chemical reactions :-

i) Combination Reaction :-  A  reaction in which a single product is formed from two or more reactant is known as a combination reaction.

ii) Exothermic Chemical Reaction :-  The reaction in which heat is released along with the formation of products are called Exothermic chemical reaction.

b) Respiration is also an Exothermic reaction.

Endothermic reaction A reaction in which energy is absorbed from the surroundings and cooling is produced is called endothermic reaction.     

iii) Decomposition reaction :-  The reaction in which a single reactants breaks down to give simple product is known as decomposition reaction.

iv) Thermal decomposition reaction :- When a Decomposition reaction is carried out by heating it is called thermal decomposition reaction.

Note :-  Decomposition reaction requires  energy either in the form of heat, light or electricity for breaking down the reactants.

Displacement Reaction :- When an element displaces another element from its compound a displacement reactions occurs.

Precipitate :-  It is an insoluble solid that emerges  from liquid solution.

Formation of Precipitate :- Precipitate can form when two soluble salts react in solution to form one or more insoluble product.

Precipitation Reaction :-  Any reaction that produces a precipitate can be called precipitation reaction.

Example :-  In the given reaction the Barium sulphate is a solid precipitate which is an insoluble substance.

Double Displacement Reaction :- The Reaction in which an exchange of Ions between the reactants are called double displacement reaction.

Oxidation and reduction

Oxidized :- if a substance gains oxygen during a reaction it is said to be oxidised.

Reduced :- if a substance loose oxygen during a reaction it is said to be reduced.

Oxidation reduction reactions or redox reaction :- if one reactants gets oxidized while the other gets reduced during a reaction, Such  reactions are called oxidation - reduction reaction or redox reaction.

Oxidation :- It is the gain of oxygen or loss of hydrogen.
Reduction :- It is the loss of oxygen or gain of hydrogen.

Corrosion :-  When a metal is  attacked by substances around it such as moisture, acid etc. It is said to be corrode and this process is called corrosion.

Example :- i) The black coating on silver.

   ii)  The green coating on copper

Methods To Prevent Metal From Corrosion :-

i) Painting the metal surfaces.

ii)  Powder coating the surfaces.

iii) Oiling the metal surfaces.

iv) Galvanization – It is the process of applying a ss protectiv zinc coating to iron or steel articles, to prevent them from rusting.

Rancidity :- Rancidity is the spoilage of food such that it becomes unsuitable and undesirable for consumption.

Food turns rancid when the fats and oils within them get oxidized and the taste and smell of the food changes. Oxidation of fats generates highly reactive molecules in the rancid food which is responsible for the unpleasant odour and flavour.

Rancidity can be prevented using the following methods:
* Adding antioxidants (substances which prevent oxidation) to food.
* Storing food in airtight containers to slow the process of rancidification.
* Refrigerating food also helps to slow down rancidification.
* Replacing oxygen in the containers with another gas.
For example, to prevent chips from turning rancid, chips manufacturers flush the bags with nitrogen gas.

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