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CHEMICAL REACTIONS AND EQUATIONS
GIST OF THE LESSON
1) Chemical reaction— Chemical changes or chemical reactions are the changes in
which one or more new substances are formed
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3) Balanced Chemical equations – The chemical equation in which the no
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4) The chemical reactions can be classified into different types such as—
a) Combination reaction – The reactions in which two or more substances combine to form a
new substance are called combination reaction
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For example,
2Pb (NO3)2 (s)  2PbO (s) + 4NO2 (g) +O2 (g)
The decomposition of a substance by passing electric current through it is known as
electrolysis
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The decomposition of a substance by absorbing light energy is called photochemical
decomposition
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For
example,
i)

Zn (s) + CuSO4 (aq)  ZnSO4 (aq) + Cu (s)
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d) Double Displacement Reactions - The chemical reactions in which compounds react to
form two different compounds by mutual exchange of ions are called double displacement
reactions
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For example
AgNO3 (aq) + NaCI (aq) -----> AgCl(s) + NaNO3
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NaOH (aq) + HCl (aq)  NaCl (aq) + H2O
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e) Redox reaction: Chemical reaction which shows both oxidation and reduction reaction
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Reduction: Reaction that shows the loss of oxygen or gain of hydrogen
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ZnO + C  Zn + CO
ZnO reduce to Zn ---- reduction
C oxidize to CO ------oxidation
f) Exothermic reaction and endothermic reaction: On the basis of energy changes during chemical
reaction, they can be classified as
i)
Exothermic reaction: A chemical reaction in which heat energy is produced
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CaCO3 + Heat  CaO + CO2

5 Corrosion – The process of slow conversion of metals into their undesirable compounds due to
their reaction with oxygen, water, acids, gases etc
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Rusting – Iron when reacts with oxygen and moisture forms red substance called rust
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This is called rancidity
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It can be prevented by using various methods such as by adding antioxidants to the food materials,
Storing food in air tight container and by flushing out air with nitrogen
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MIND MAP

BALANCI
NG

WRITIN
G

CHEMICAL
EQUATION

CHEMICAL
REACTION
EXOTHERMIC-release heat
ENDOTHERMIC-absorb heat

COROSSION
Eating away of
metals

RANCIDIT
Y

REDOX
REACTION
Show both oxidation
and reduction

TYPE OF
CHEMICAL
REACTION

Oxidation
of fats and
oil

DOUBLE
DISPLACEMENT

Two different
atoms or group of
atoms displaces
each other
AB + CD  AC +
BD

COMBINATION

Two more
substance to
give single
product
A+BC

DECOMPOSITION

DISPLACEMENT

Single substances
decomposes to
give two or more
new substances
AB+C

More reactive
element displaces
less reactive
element
A + BC  AC +
B

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PAPER
MARKS-30

TIME- 70 MINUTES

Instructions:
 Questions : 1 to 5 – 1 Mark each
 Questions : 6 to 9 – 2 Marks each
 Questions : 10 to 13 – 3 Marks each
 Question 14 – 5 Marks
1
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Identify the compound oxidized in the following reaction:
H2S (g) + Cl2  S (s) + HCl (g)
3
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4
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5
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Explain the following in terms of gain or loss of oxygen with one example:
a
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Reduction
7
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Why do we apply paint on iron articles?
9
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What is rancidity? Write the common methods to prevent it
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What is corrosion? State the conditions necessary for rusting of iron
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Name the type of reactions in the following cases:
a
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Burning of natural gas
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Carbon dioxide gas passed through lime water
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Blue crystals of copper sulphate on heating in a dry test tube become colourless
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a
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Why is it always essential to balance a chemical equation?
c
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Can rusting of iron take place in distilled water?

HOTS QUESTIONS (SOLVED)
Q
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Ans
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2
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Q
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Ans
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When the gas was passed through water,
the solution obtained turned blue litmus red
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Identify the substance ‗X‘
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The water insoluble substance ‗X‘ is metal carbonate CaCO3
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The white powder
formed was taken in a test tube and water was added to it
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What change was seen? Why?
Red litmus paper turned blue
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This is because the magnesium ribbon on burning in air forms the white magnesium
oxide
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Give one example of a combination reaction in which an element combines with a compound
to give you a new compound
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4
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Assign a suitable
explanation
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5
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Explain why?
Rancidity is a process used for spoiling of cooked food materials like vegetables, etc
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How can you prevent such process to proceed? Give an example
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It is called displacement reaction
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It reacts with dil
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What is the gas evolved? Calculate the minimum amount of ‗Z‘
required to produce 100 l 0f gas?

Q
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7

Q
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Q
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Q
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Q
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Q
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Name the element ‗X‘& black the coloured compound formed
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Oral questions (Conversation type)
a) How do you represent chemical changes in chemistry?
b) What should you know to write a chemical equation?
c) How are reactants and products separated in a chemical equation?

2
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a) What happens when calcium carbonate is heated?
b) What is this reaction called?
c) Does decomposition take place only on heating?

4
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5
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c) What are the requirements for corrosion?

1
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To pack food articles, why do manufacturers flush out oxygen with nitrogen?

3
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What is the chemical reaction called in which heat is evolved?

5
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Name the phenomenon
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Which gas is evolved when acid is added to lime water?

7
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