class 10 chemistry chapter 1 notes

                                                                   CHAPTER-1

INTRODUCTION

1. Most of the substance around us undergoes various changes.Some of these changes are temporary with no new substance being formed . They are called physical changes .

2. In certain other changes the new substances formed in which the reactant  loses its  identity to form new substance called product. These changes are permanent as we wan't get the reactant back.

CHEMICAL REACTION

Chemical reaction process by which two or more substance react with each other to form new substance with different properties.

These are the following changes to determine that the chemical reaction has taken place:

(i)   change in state

(ii)  change in color

(iii) evolution of gas 

(iv)  change in temperature

CHEMICAL EQUATION

 A chemical equation is the symbolic representation of a chemical in the form of symbols and formulae where in the reactant entities on the left-hand side and the product on the right-hand side.

FOR Eg: MAGNESIUM+ OXYGEN → MAGNESIUM OXIDE

BALANCED CHEMICAL REACTION

A chemical reaction that shows the chemical reaction need to be balanced. A balanced chemical equation occurs when the number of atoms involved in the reactants side is equal to the number of atoms in the products side.

TYPES OF CHEMICAL REACTIONS

1. Combination reaction- Such a reaction in which a single product is formed from two or more reactants is known as a combination reaction.

Calcium oxide reacts vigorously with water to produce slaked lime releasing a large amount of heat.

Reactions in which heat is released along with the formation of products are called exothermic chemical reactions.

2.Decomposition Reaction-  When single reactant breaks down to give simpler products. This is a decomposition reaction.

Decomposition of calcium carbonate to calcium oxide and carbon dioxide on heating is an important decomposition reaction used in various industries. Calcium oxide is called lime or quick lime. It has many uses- one is in the manufacturing of cement.When a decomposition reaction is carried out by heating, it is called thermal decomposition.

When silver chloride turns grey in sunlight. This is due to the decomposition of silver and chloride by light.

3.Displacement Reaction- Displacement reaction is a chemical reaction in which a more reactive element displaces a less reactive element from it's compound.

Both metals and non- metals take part in displacement reaction. Reaction of iron nail with copper sulfate solution.

Double Displacement Reaction- A double displacement reaction,also known as a double replacement reaction or metathesis, is a type of chemical reaction here two compounds react and the positive ion and the negative ion of the two reactants switch places forming two new compounds or products.

4.- Redox Reaction- An oxidation-reduction reaction/redox reaction is a type of chemical reaction that involves a transfer of electrons between two species. An oxidation-reduction /redox reaction is any chemical reaction in which the oxidation number of a molecule, atom or ion changes by gaining or losing an electron.

Oxidation:This process involves gain of oxygen or loss of hydrogen.

Reduction: The process of gain of hydrogen or loss of  oxygen.

OXIDIZING AGENT- It is the substance which gives oxygen or gains hydrogen.

REDUCING AGENT- It is the substance which gives hydrogen or gains oxygen.

CORROSION

The process of slow conversion of metals into their undesirable compounds due to their reaction with oxygen , water , acid gases ,etc. present in the atmosphere is called corrosion.