Chapter 1: Chemical Reactions and Equations

Chemical change – one or more new substances with new physical and chemical properties are formed.
 

Here, when copper sulphate reacts with iron, two new substances, i.e., ferrous sulphate and copper are formed.

A chemical equation is a statement or representation that describes a chemical reaction in terms of
symbol and formulae.
➢ A chemical reaction is the transformation of chemical substance called reactants into another chemical
substance called products. In a chemical reaction, only rearrangement of atoms takes place.
➢ The substances which take part in a chemical reaction are called reactants. The reactants are written
on the left hand side. The new substances produced as a result of chemical reaction are called
products. The products are written on the right hand side.

Some of the symbols used in a chemical Equation are :
(a) Solids (s)
(b) Liquids (l)
(c) Gases (g)
(d) Aqueous solutions (aq)
(e) Gas released as a product (↑)
(f) Precipitate formed in the reaction (↓)
(g) Direction of reaction (→)
➢ Steps to balance a chemical equation :
(a) Write word equation.
(b) Then write skeletal chemical equation.
(c) Enclose the formula in the boxes.
(d) List the number of atoms of different elements present in the unbalanced equation.
(e) Start balancing with the compound that contains the maximum number of atoms.
(f) Start balancing other atoms.
(g) Check the correctness of the balanced equation.
 

 

NCERT Solutions -Class 10 -Chemical Reactions and Equations

 

Chemical Reaction

When two or more substance react with each other to form one or more new substance this is called chemical reaction

 

The substances which reacts with each other in a chemical reaction are known as reactants they are generally written on the left hand side of the equation

 

The substances which are formed in a chemical reaction are known as product they are generally written on the right hand side of the equation

 

Chemical reactions can be of different types

 

1) Combination reaction-- when two or more substances combine together to form a new substance is called combination reaction

 

Symbolically

 

A+B ------C

 

Two substances A and B are combined together to form a new substance C

 

Example

 

H2+Cl2------2HCl

 

2) Decomposition reaction-- when a substance decomposes into two or more substances is called decomposition reaction

 

Symbolically

 

C---A+B

 

The compound C decomposes to two compounds A and. B

Example

 

ZnCO3------Zn + CO2

 

 

The composition of a compound can be done by either of the methods

 

 --- by thermal decomposition 

--- by electrolysis 

-----by photolysis reaction 

 

3) Displacement Reaction 

 

When an element of a compound displaces by another element during a chemical reaction is known as displacement reaction

 

Symbolically

 

AB+C-----AC+B 

 

In above equation element C displaces element B of the compound AB so this type of reaction is known as displacement reaction

 

2HCl+Mg------MgCl2 + H2

 

 

4) Double displacement reaction

 

When elements of compounds and exchanged each other in a chemical reaction what is known as double displacement reaction

 

Symbolically

 

AB+CD-----AD+BC

 

In the above reaction elements of the compound AB and elements of the compounds CD are exchange together to form a compounds AD and BC

 

2KBr+BaI2-------2KI. + BaBr2

 

Types of reactions positive ion of one compound reacts with negative ions of another compound similarly in negative ions of the first compound combines with positive

Redox Reaction

The reaction in which there is a oxidation and reduction both occurs is known as red oxide reaction in this type of reaction there is gain of electron in one element and loss of electrons in an atom

 

The element which gains electrons undergoes oxidation reaction it can also be defined as addition of oxygen is known as oxidation reaction

 

The element which loses electron undergoes reduction reaction or in other words addition of hydrogen is known as reduction reaction

 

The substance which undergoes oxidation is known as reducing agent

The substance which undergoes reduction is known as oxidising agent

Limiting Reagent

The substance which consumes completely in a chemical reaction is called limiting reagent generali on limiting reagent decide the extent of a chemical reaction

 

 

Notes by teacher 

note by teacher

Sagar Daksh Science Book > Unit I: Chemical Substances - Nature and Behaviour > Chapter 1 Chemical reactions > Implications of a balanced chemical equation.

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