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CLASS- X
SUBJECT-SCIENCE

TOPIC-CHEMICAL REACTIONS
AND EQUATIONS

Short Notes Made By Rajrupa Roy

Topics to be covered
❖ Writing a Chemical Equation
❖ Balancing Chemical Equation
❖ Types of Chemical Reactions
❖ Corrosion
❖ Rancidity
❖ Practice Problems

Definition Of Chemical
Reaction
A chemical reaction is a process that leads to the
chemical transformation of one set of chemical
substances to another
...
The reactants are written on
the left-hand
side (LHS) with a plus sign (+) between them
...

The arrowhead points towards the products, and shows
the direction of
the reaction
...

Steps of writing a chemical equation and balancing its reaction
Identify reactants and products and place them in a word equation
...

Balance the chemical equation
...
Write the unbalanced equation to show the reactants and products
...
Write down how many atoms of each element there are on each side of
the reaction arrow
...
Add coefficients (the numbers in front of the formulas) so the number of
atoms of each element is the same on both sides of the equation
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4
...


Balancing Chemical Reaction with(Ex)
The first step is to write down the unbalanced chemical equation
...
To write the reaction, you need to identify the
reactants (iron and oxygen) and the products (rust)
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For example, O 2 has 2 atoms of oxygen
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There is 1 atom in Fe
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On the reactant side:
1 Fe
2O
On the product side:

2 Fe
3O

When balancing equations, you never change
subscripts
...
Coefficients are whole number
multipliers
...
As with subscripts, you don't
write the coefficient of "1", so if you don't see a coefficient, it means
there is one molecule
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There is one atom of iron on the left and two on the right, so you
might think putting 2 Fe on the left would work
...
By inspection (i
...
, looking at it), you
know you have to discard a coefficient of 2 for some higher number
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4 Fe works, if you then add a coefficient of 2 in front of the rust (iron
oxide) molecule, making it 2 Fe2O3
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Next you need to balance oxygen
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The reason is that they
usually appear in multiple reactants and products, so if you tackle
them first you're usually making extra work for yourself
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If you put a 2 in from of O2, that will give
you 4 atoms of oxygen, but you have 6 atoms of oxygen in the product
(coefficient of 2 multiplied by the subscript of 3)
...

If you try 3 O2, then you have 6 oxygen atoms on the reactant side
and also 6 oxygen atoms on the product side
...

Remind the audience what you covered in the
previous slides
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(i) Hydrogen + Chlorine →
Hydrogen chloride

(ii) Barium chloride + Aluminium
sulphate → Barium sulphate +
Aluminium chloride
Problem Time!!!!

(iii) Sodium + Water → Sodium
hydroxide + Hydrogen

TYPES OF CHEMICAL REACTION
...


Ex-Calcium oxide reacts vigorously with water to produce
slaked lime
(calcium hydroxide) releasing a large amount of heat
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Ex-2FeSO4(s)

Fe2O3(s) + SO2(g) + SO3(g) (1
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When a decomposition
reaction is carried out by heating, it is called thermal
decomposition
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Displacement Reaction
A displacement reaction is a type of reaction in which part of one
reactant is replaced by another reactant
...
24)
(Copper sulphate)

(Iron sulphate)

Double displacement
Reaction

Reactions in which there is an

exchange of ions between the reactants are called double
displacement
reactions
...
Such reactions are called oxidationreduction reactions
or redox reactions
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This process
is commonly known as rusting of iron
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Have you noticed the colour of
the coating
formed on copper and silver? When a metal is attacked by
substances
around it such as moisture, acids, etc
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The black coating on silver and
the green
coating on copper are other examples of corrosion
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Usually substances which prevent
oxidation
(antioxidants) are added to foods containing fats and oil
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