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CHAPTER – 1

Chemical Reactionsand Equations
q

Chemical Reaction : – Whenever a chemical change occurs we can say that
a chemical reaction has taken place
eg

q

–

Food gets digested in our body

–

Rusting of iron
...


q

Physical state of the reactant and products are mentioned to make chemical
reaction more informative
...


q

Balancing Equation :– We balance the chemical equation so that no
...

eg Fe + H2O

→ Fe2O3 + H2 can be written as

3 Fe(s) + 4H2O(g)
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→ Fe2O3(s) +4H2(g)

Combination Reaction :– The reaction in which two or more substances
combine to form a new single substance

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eg


→
CaO(s) + H2O(l)
Ca(OH)2 (aq)
Calcium
Water
Calcium hydroxide
oxide
(slaked lime)

Quick lime
–

Ca(OH)2 slaked lime is used for white washing walls
...

Ca(OH)2

–

(aq)+

CO2


→
(g)

CaCO3

(s)+

Calcium

Calcium

hydroxide

Carbonate

H2O (l)

Burning of Coal
C(s) + O2(g) → CO2(g) + heat + light

–

Formation of water
2H2(g) + O2(g) → 2H2O(l)

q

Exothermic Reactions :– Reaction in which heat is released along with the
formation of products
...
CH4(g) + 2O2(g) → CO2(g) + 2H2O(g)

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–

Respiration is also exothermic reaction
...


De compositon Reactions :– The reaction in which a single substance
decomposes to give two or more substances
...


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–

Endothermic Reactions – The reactions which require energy in the form
of heat, light or electricty are called Endothermic Reactions
...


–

Other examples

Zn(s) + CuSO4 → ZnSO4 + Cu(s)
(aq)

(aq)

Copper
Sulphate

Zinc
Sulphate

Pb(s) + CuCl2 → PbCl2

–

+ Cu(s)

(aq)

(aq)

Copper
Chloride

Lead
Chloride

Zinc and lead are more reactive elements than copper
...

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Double Displacement Reaction : The reaction in which two different atoms
or group of atoms are mutually exchanged
eg
...
The insoluble substance
is called precipitate
...

eg
...
2Cu + O2 
When Copper is heated a black colour appears
...


–

Redox Reaction : The reaction in which one reactant gets oxidised while
other gets reduced

eg
...

eg
...


(ii)

Black coating on Silver
...


–

Antioxidants are added to foods containing fats and oil
...


What happens when the milk is left at room temperature during summer?

2
...


3
...


Why do copper vessels lose their shine when exposed to air?

5
...


Fe2O3 + 2Al → Al2O3 + 2Fe
The above reaction is an example of which type of reaction
...


Name the type of reaction in which energy is absorbed
...


Why does the colour of copper sulphate solution change when an iron nail is
dipped into it?

9
...


10
...


Write down the observations which indicate the occurence of a chemical
reaction
...


Why is respiration considered as an exothermic reaction? Explain
...


Transfer the following statements into Chemical equations and then balance
them
...


a)

Hydrogen gas combines with nitrogen to form ammonia
...


Identify the substances that are oxidised and the substances that are reduced
to the folllowing reactions
...


Na

+

O2

(s)

(g)

CuO

+

(s)

H2


→ Na2O

(s)

(g)


→ Cu + H O
2
(l)
(s)

5
...
Write the equation also
...


Why is the bag used for potato chips flushed with nitrogen gas?

Answer the following questions in detail
1
...

a) Zinc Carbonate(s) → Zinc Oxide + Carbon Dioxide(g)
b) Aluminium(s) + Chlorine(g) → Aluminium Chloride(s)
c) Magnesium(s)+ Water(l)

2
...

+ 4HCl(l) → MnCl2

i)

MnO2

ii)

CaO

iii)

2AgCl(s) → 2Ag(s) + Cl2

(s)

(s)

+ CO2

(g)


→ CaCO3

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(s)

+ Cl2

(g)

+ 2H2O

(l)

(s)

(g)

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3
...
Write the type of reaction that has occured
...


(5 marks)

Balance the following chemical equation and identify the type of reaction they
represent
KClO3 → KCl + O2
NH3 + O2 → NO + H2O
Na2O + H2O → NaOH
Na + H2O → NaOH + H2
FeCl3 + NaOH → Fe (OH)3 + NaCl
...


Define various types of chemical reactions
...


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