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. . Chapter • l Chemical Reactions And
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--~ -~ •-----·-------~:..•• ~- •-i . Equations

. T he proces~ in which new

substances with new properties
formed from one or more substanc are
es is called Chemical Reaction.

* The substances which take pa

rt in chemical reaction are called
Reactants.
* The substances which are formed
in a chemical reaction are called
Products.
,
....--~ ....---,-~
Examples: f

(il Digestion of food

(ii) Respiration
I

r
(iii) Rusting of iron
(iv) Burning of Magnesium ribbon
(v) Formation of curd 1
... .-·.- .....
---~ . . . ,

Ch em ica l re ac tio n in vo lve s :

• Change in state '

• Change in colour
• Change in temperature
• Evolution of gas
Science Class - 10
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 Ways of Representing a Ch em ica l Reaction .

Word Equation
Zinc + Sulphuri_c Acid -+ Zinc sulphate + Hy~rogen
lL --. ... --- --- --- -

LHS RHS •
., (Reactant) (Pfodu~t)
~hemical Equation
Zn + H2S04 --+ ZnSO +
4
I.
l -
LHS RHs
(Reactant) (Produ
Chemical Equatio~
* A chemickl rea~tion can be represented
by chemical equatio
. It involves uses of symbol of elements or chemical form
ula of reacta
and product with ~ention of physical state. ·
* Thenecessaryconditionssuchastemperature,pressureoranyc
• '
ataly
should be written on arrow between reactant and pro
. ,
~ucts.
e.g., Magnes_ium is bu_rnt in air to form Magnesium oxide.
. .
.. 2M g+02-+ 2Mg0
. .
.
Bal an~ ing Ch em ica l EC{Uation·
, .
* Law of con~ervation pf M~ss : Matter can
I

neither be created no
be destroyed in a ·chemi~al reacti9n. • .
. . .
* So number: of e!ements involved in chemical
reaction should remai
same at. reactant and product side. .. .• '/
.. ,• \

STEPWISE BALANCING (Hit and Trial)

Step 1. Write a che~!ca~equ~~o.n 1nd i~~aw ~ox~s-~

~~und each fofIIlula.
. I Fe + ' H O 1-+ Fe O 1+ 1 H i•
. ..1 . •-·-- 2 ·-·-: •···----3....4J L__ 1 .J
* Do not cha
. nge anythin
. g inside the box.
. .
. .
Step 2 . Count the_ number of atoms. of each element
\
.

on both : • .
chemical equation. • • . the sides o
. .. Science Class-.10 •• .....
_... --· .\.
 Element No. of atoms at No. of atoms at .
reactant side . .. pr_oduct side
1. Fe •. 1 3
2. H· . . . 2 , 2
. 3. 0 1 .. ··4 .:
, Step 3. Equalise the number of atoms of element which has maximum
number by pµtting in front of it. .
. [Fe ] + [48z<>l-fFe + ~-~, • : •
Step 4. Try to equalize all the atoms of elements o·n reactant and product
side by adding coefficient in front of it. • • • '••
• • [ 3F~ + 1. 4~·;6] .... [Fe;_o
4..] + f 4H;1 •.
* Now al~ the atoms of elements. are equal oil both sides.
Step 5.Write the physical states of reactants and products.
3Fe (s)'+ 4820 (g)-:-+·Fe 30 4 ( s) + 482 (g) ·
Solid state= (s) •

Liquid state=(/) ·, ,

. Gaseous state = (g)

Aqueous state = (aq) •
. .
Step 6. Write necessary conditions of temperatur~, pressure or catalyst on ··
arrow above or below. • • ••
.
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TYPES OF CHEMICAL REACTIONS
• . . , .. . .
., . :

I. CO MB INATION REACTION :The reaction in which two or more reactant

combine to form a single product~ ·_.·. • : • ••
. -- .. . • ......-~......-.~· ---.-.. .....- e.:-ur,
e.g. (i) Burning of coal •
. C (s) + 02(g)-. CO2(~)
(ii) Formation of water
2H2 (g) + 0 2 (gJ-. 2H20 (I)
(iii) Cao (s) + H20 (I)-. Ca(OH) 2 (aq) ...
Quicklime Slaked lime . , \
..
,

Exothermic Reactions : Reaction in which heat is released along with

formation of products. . .. •

• Science Class - 10
e.g., (i) Burning of natural gas
CH 4 (g) + 0 2 (g) --+ CO 2 (g) + 2H 2O (g) + Heat
(ii) Respiration is also an exothermic reaction.
C6H12O6 (aq) + 602 (g)--+ 6CO2 (aq) + 6H 2O (I)+ energy
----~
11. DECOMPOSITION REACTION: The reaction in which a compound sp}i
into two or more simple substances is called decomposi tion reaction.
A~B+C
• Thermal decompos ition : When decomposi tion is carried out
heating.
. Heat
e.g., (I) 2FeSO4 (s) >Fe2O3 ( s) + SO2 (g) + SO3 (g)
(Ferrous sulphate) (Ferric oxide)
Green colour Red-brown colour

(ii) CaCO3 (s) Heat )CaO (s) + CO2 (g)

(Lime .stone) (Quick lime)
(iii) 2Pb (NO 3) 2 Heat > 2PbO+4NO2(g)+O 2
-~ Oead nitrate) (lead oxide) (Nitogen dioxide)
• Electrolyt ic Decompo sition: When decomposi tion is carried out
passing electricity.

Electric
e.g., 2H 20 + 02
current

~....._-__ ,,i,~~,-.-P lastic mug

Oxygen Hydrogen

Test tube Water

Graphite rod---.~.. ......~water

,,___ _ _ Rubber Stopper

Anode- -....... .a----- Cathode

Switch ---- ___,L.<r_

• Photolytic Decompo sition : When decomposition is carried out·

presence of sunlight.

Science Class - 10
 e.g., • 2AgCI (s) Sunlight (s) + Cl (g)
2

2AgBr (s) Sunlight )2Ag (s) + Br2 (g)

Silver chloride turns grey on exposure to sunlight •
* Above reaction is used in black & white photography.
• Endothermic Reactions : The reactions which requi_re energy
in the form of heat, light or electricity to break reactants are
called endothermic reactions.
III. DISPLACEMENT REACTION· : The chemical reaction ini•which more
reactive element displaces less reactive element from
. .its salt
.
solution.
Fe (s)_+ CuS04 (aqJ-. FeSO~ (aq) + Cu (s).

Stand ......

a---·Testtube
....-tii--- Thread .
. .
--lll.:opper sulphate
solution . -
--Iron nail

. , .. . .

•. . -·•. ""'
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The iron nail becomes brq-wnish in col0ur :by· deposition of Cu and blue
., ,•.

t?
colo~r of CuSO4 changes dirty ,gr~e.~-_col~ur due to ~ormation of FeSO4•
.. Zn+ Cu5Q4~ Zn~O 4 ·-+ Cu
• • . • . I' .... .. •·•· I · • '.

•
zn·is more reactive than copper.·:. ::. ,·, :• . •
• ·~•:,-) , I. , ~- , .. : - .•• • ,· • . .

IV. DOUBLE DISPLACEMENT REACTION : A reaction in which new

compounds are formed:. by· mu~1:1a(. e~change of ions between two
compounds. •
,. 1, ... ' • J ' , • • •• ..

(i}. Na2S04 (aq) +. BaCl2 (aq) ··:-+_BaSO 4 (s) + 2NaCI (aq)

I (Sodium .~_,:-} {Barium. (Barium (Sodium I:·

sulphate) . • chloride) - sulphate) . chloride)

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white precipitate of BaS~4 -is formed, so it is also called p·recipitation

reaction.
Science·Class - 10
 (ii) 2KI + Pb(NO3)2 -+ +Pblz +2KN03
• (potassium Iodine) (Lead Nitrate) . •(Lead iodide)
(Potassium nitrate) (Yellow ppt) (Yellow ppt.)
(iii) 2KBr+Bal2 -+ 2KI + BaBr2 • . . . ..
(Potassium Bromide)+(Barium iodide) __. (Potassium 1od1de) . + (Barium bromide)
V. OXIDATION AND REDUCTION : . , .
Oxidation : (i) The ~ddition of oxygen to reactant.
'
(ii) The removal of hydrogen from a reactant. .
C + O2--._CO 2 .

2Cu +0 2 Hea_t > 2Cu0 · • I

Heat ·
CuO + H2 .>Cu+ H20
Reducti~n : (i) The addition of hydrogen to reactant.
(ii) The rem.oval of oxygen froi:n reactant.
• oxidation
I
CuO + H Heat > Cu+
.
H20
t
2
. I .•
Reduction . . .
,n this reaction cu9 is reduced to Cu and H2 is oxidized to H2O. So,
oxidation and reduction taking place_ together is re~ox reaction.
Effects of qxidation in Daily Life
1J Corrosion

• When a me~l is exposed to· moisture, air, acid etc~ for some· time,
a layer of_hydrated oxi~e· is forme~ which weakens the metal and
hence metal is said to be corroded:
. .
• Rusting ofiron, black coating on silver and green coating on copper are
examples of corrosion.
' . • .• •. •
• ·corrosion can be prevented by_galv~nization, electroplat1qg or by
p~tting paints. • •
2) Rancidity: The oxidation of fats.and dils when exposed to air is known as
rancidity. It leads to ~ad smell and bad taste of food.
Methods to P~vent Rancidity
(i) . By adding antioxidants
(ii) Keeping ~ood in air tight containers
-~ , Science Class - 10
 (iii) Replacing air by nitrogen
•-
(iv) Refrigeration

QUESTIONS
VERY SHORT QUESTIONS (1 Mark)
. Q.1 The shiny finish ofwall after white wash is because of.
a) Calcium oxide b) Calcium hydroxide •
c) Calcium Carbonate •d) Calcium phosphate
Q. 2 Electrolysis of water is decomposition reaction. The mole ratio of
hydrogen and oxygen gases liberated during electrolysis ofwater is
a) 1:1 b) 2:1 . c) 4:1 . d) 1:2
•Q. 3 Which the following statements about the given reaction are correct:
, I

3fe(s) + 4H 20 (g) Fe20 3(s) + 4H2(g)

i) Iron metal is getting oxidized
ii) Water is getting reduced
iii) W~ter is acting as reducing agent
iv) Water is acti.ng as oxidizine agent
a) (i), (ii) and (iii) b) (iii) an~.(iv)
c) (i), (ii) and (iv) d) (ii) and (i'v).
Q. 4 • In order to prevent the spoilage of potato chips, they are packed in
plastic bags containing the gas ( '

a) Cl2 b) 0 2 c) N2 d) H~ . "

'.
Q. 5 The process of respiration is·-
. . ·•
a) an oxidation reaction which is endothermic •.r
\ ...
b) a reduction reaction which is exothermic
'
c) a combination reaction which is endothermic • ·_ '. .
1

d) an oxidation reaction which is exothermic

.
Ans 1 (c) 2 (b) 3 (c) 4 (c) 5 (d)
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r Science Class - 10 • • ··~ • ··-1

. _____..,.....,.,._......,.J
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Q. 6 Gi\Te an exa'mple of double diSplacE!inent reaction? (CBSE 2010, 2011)
Q. 7 Name the reducing agent in given below che~ical reaction
' •
3 Mn02 4Al . . >3 Mn+2Al 20 3 (CBSE-20i6)
Q.8 Name the brown coloured gas evolved when lead nitrate crystal are
' heated in dry test-tube.
Q. 9 Give reasons- •
a) Silver chloride is stored in dark coloured bottles•
•
_b) CopPervesst?l loses shine when exposed to air •
. .
: . c) Iron•is places copper frQm copper sulphate solution.
. . It
Q. 10 I~entify the following reactions as
, . Ocombination ·ii) decomposition ~ii) displacement

I reactions and double displacement reaction.

i) ZnCO3 (s) > ZnO(s) +· CO 2 (g) ,
ii) Pb(s) + CuCl2 >PbCl2 (aq) + Cu(s)
iii) H2 (g) + a2 (g) . . > 2HC1
. . .
. .. . . . . iv) Ca~o3 (s}·. Cao (s) +. CO 2 (g)
.. . • • • t
>
•

v)NaCl(g)+AgNO3 (a) > AgCl+NaNo 3

vi) 3H; (g) + N2 (g} • > 2NH3 (g) .

-vii) Fe2O3 +Al • > Al2O3 +2Fe -: ·• •
' . ,
11. •What changes. do you obse~ e in the iron_ nails and colour of copper
sulphate soluti
.
on, if iron· nails. ··are. dipped in CuSO solution for 15
• 4 •
minutes? • • . ., -.
12. Identify the chemical. change : . . J• • • ••
I •

Melting of ice or conversion ~f milk into cu~d.

13. Why is respiration conside~ed an exothermic reaction ?

14. Why do copper vessel lose shine when exposed to air ?

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:,···:Sc
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ience Class - 10 • · ., ..
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15. Potato chips manufacturers fill the p~cket of chips with nitrogen gas.
Why?
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, • l

.16. Why we store silver chloride in dark coloured bottles in labs?

17. Write a chemical equation of double displacement reaction.

18. N2 + 3H2 -+ 2NH 3, name the type of reaction.

\

19. What happens when milk is left open at room temperature during
summers?

20. What happens when quick lime is added to water?

Practice Based MCQ's
1. When aqueous solution of sodium sulphate and barium chloride are
mixed together, it becomes-
. a) turns red b) forms a white precipita
, .te .,
c) forms yellow precipita~e d) becomes co~ourless
2. •The colour of ferrous ~ulphate crystal is-
, .
a)
.
yellow b) light green . c) red d) brown
. .
3. Astudent took solid quick lime in a china dish and added a small amount
. ofwaterto it. He would hear-.
a) pop sound b) a crackling sound • ·
c) hissing sound :· d) nosou~datall . •
4. When an iron nail is placed in copper ~ulphat~ so)ution the obs_ervatiori
are as follow-· • •·
a) The solution,turns light green .
-. . .
b) Abrown deposit is formed o_~ the nail
c) Born 'a' and 'b'
d) Noneoftheab_ove
Answer
1. (b)
2. (b)
3. (c)
4. (c)

Science Class 10
 SHORT TYPE QUESTIONS (3 Marks)

1. Define combination reaction. Give· two examples of combination

reaction which is exothermic in nature.

2. •What is decomposition reaction? Explain with the help of an example.

3. Name and state the law which is kept in mind when we balance a chemical
equation!
4. Give one example of.each :
·(a) Chemical reaction showing evolution of gas.
(b) Change in substance's colour during a chemical reaction.
I

(c) Chemical reaction showing change in temp.. •

5. What is rancidity? Write two ways by which it can be prevented.
6. What are two· conditions which promotes corrosion ?
7. A small amount of Ferrous sulphate is heated in hard glass tube.
(a) Write the chemical equation.
(b) What type of reaction is taking place.
' .
8. What happens w~en Zn strip is dipped in CuSO4 solution ?
Give equation and i_dentify the type of re~ction.
9. What is redox reaction ? Write do_wn a chemical reaction representin
it .
10. In electrolysis of water': . •

(a) Name the gas collected at·cathode and anode.

(b) Why is volume of o~e gas collected at one electrode is double o
. another?

11. •(c) Why are few drops of dil. H2S04 added to water ?
In the reaction

CuO (s) + H2(~)-. Cu(s) + H20 (g)

Science Class - 10
l~
i

(a) Name the oxidized substance.

(b) Name the reduced substance.

(c) Name th~ oxidizing agen~.

• I

12. 'G'ive reasons:

.(a) White Sil;erchloride t.urns grey in sunlight.

•(b) Brown cqloure~ copper powder o~ heating in air turns into black
) coloured.substance. •

13. Compound 'X' decomposes to form compound 'Y' and CO gas.

2
Compound' Yis used in manufacturing of cement.

(a) Na'!le the co~pounds 'X' and 'Y'. ;

\

(b) Write the chemical equation for this reaction.· •

• 14. A metal salt MX when exposed t~ light splits up _to form metal M and
gas X2• Metal M is used to ~ake o'rn~ments whereas' gas X ,is used
2
in makin g bleaching powde r. The salt MX is used in black & white
' . .
. . -
photography. •
.•

. .
(a) Identify the.metal Mand gas X •
2

(b) Identify MX.

.
(c) Write down t~e chemical reaction when salt MX is exposed to
.

_sunlight.
' . .
15. A metal strip X is dipped in ~lue co~oured salt solution YSO • Aft~r
4
some time a layer of me~al 'Y' is formed on metal strip X. Metal X is
. .
used in galvanizat~o·n whereas metal Y is used for making electric
.- wires.

.
-r .
'
Science Class - I 0
 (a) What could be metal 'X' and 'Y' ?

·• (b) Nam~ the metal salt YSO4, •

(c) \Vhattype of chemical r~actio_n ta~es place ~etween,X_and Yso

Write the balan.ced chemical equation. 41
• ··. ,, •
Q.16 When potassium Iodide solutio~l°is added to a solution oflead nitratet
.
..
test tube, a precipitate is formed.
i) State the colour precipitate
\

ii)_N~me the compound precipitat~d .

. ' .
• •

iii) Write balanced equati~n for'chemical reaction'(CBS~-~015 Comptt)

"" • I •

. . ,
_·. _q. t7 Decompositio~ reactions· requi,re ·energy eithe~ in form of heat and Ii~
. .
. '
a electricity for breaking down of reactions. Write one equa
• 1,.
• tion for eac I

type of decomposition reaction where heat, light' or electricity is used

. • I
• l ,I • •
,.

form of ~nergy..
- Q.18 2 gm o'f silv~r chlorid~ is"take~ in chi~a dish, a~d china dish is placed i
•. sunlightf~rsometime. What will b~yoµr observation. Write the balance
. . .
chemical equation
. for above·reaction and identify the type of reactio
.

,•

.. (CBSE-2019)' • . , • I

. .
, Q.19 Identify t11e type of-reactions taking place in each of following ca~es an
.\

. .
, I ,

, . write the balanced chen_i.ical equation for the reactions.

. .
.
. ' . '
a) Zn reacts With sHver nitrate to produce zinc nitr~te an~ silver
.
.
•
. I, •
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. •, • I .
b) Potassium iodine reacts with lead Qitrate to produce potassiu
• •

. .
---" nitrate and lead iodide (CBSE-2019)

. .
Science Class - 10 •
 , I• • • • i • I
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' II

·. • .\ . • • . • . •• .' • .LONG TYPE QUESTIONS (5 M~rks) . ,'

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• '

l. Whit,e wash was being :do~e at Mukesh~s ·house. Mukesh saw that the
- • ' . ' ·•

.• •~ainter
.
a~ded quick
.
lim~ to .
drum having water. Mukesh touched outer ··
s~rfac~ of-drum, it is unbelievably hot. . I· .
' I' .. ,I .' .> •

I ·;
•/

. (a) .. Write the ~hemical equation 'for above reactt'on: ; •• _:

. .., . . • I . • . I

• .. (b) •• ~at type·of r~action is ft?·· '· : - . •, ·. ·.· ::

. .. 1

..
•(c) , _What is utility of this r~action ? • · . y , ·, • ·; • • . - -. • • • • .'

•
•
. '

,
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;
f '

.
• •

.
. .. I
• ••

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2. . Write _do~n the b~Ianced c~emical ·equa!i~ri for the following~ .- , .

t • • • • • • , •
• -. . "' I '
( • •• •. ;,. • . .,'- "' I ,, r .. , • • ,,

•(a) -~ilver· chloride is deco~p~sed in presenc·e ·of sunlight-to give . _: ·:

I • < ...... • • . •• {

', . silver and chlorine gaS.-· . : ' • . • .' : . . ': .- ' . '. '. •. •
• • ! . . • • • • JI , • , • ..

' , • ... . •. . ..,

. "
. . '/ ' . • '
. • J

(bl, ,_. ~al~i\lm oxi~e reacts wit~ j\fatei- t(}give li~e ~a~er. . .: _. ·-: .• _. . ..
, • ,• ' • •
,. ' • • ,' • • •
" • I
r {
·.

...
. • (cl ... s·odium hydroxide reacts with-' hydrochioric acid'. to.. give •.• . . .
• • ' 4 :. •
I
• ,. • • •\ .. ,. • , ., • ' • • - / • , J • .. .. J . .

sodium chloride and water. • · . • .· • ·: • · . ,: ' -· · ,-•· • •. •

•• < •~: •• I ' • ' : • ' •. • • • • •( : • • • • • • ( • • • • • ' • • ••• •• • ;, • •,. r • • •.~ :, : !•: • / ., ' : : • •

•: ~· (d) •Dif hyd~ochloric·. acid :.·is added: to copp.er oxide to give· green
• • ,, ) • .. • I' '\ • \ • - • • • •

:- • . . colpured copper chloride and watf:?r~ : /... ·. • ·:.- r. . ·:. • •\ • •. . ·, ;,- . .

.. • • • • ) • • • ,. ., . 111 .. • • • •

• • ' • • • • •• • , • ':. •• ,, , ' ' : • • • , ' .- • ' •• > :-. • - • •

_. (ej'- ' s.OlutiOn of bariu~ Chlofid~, arid. sodiUm Sulj,hate·: in" Welter _<: . · _-_
•. :·._· ,. ~:·\·~·.~reacts tp give- ~ns9l~~le Ba[~U.~~~~lph~~e a~d sol~tion. o,~ Sodium ·
• ' • ' : ,,,I • • ' ,, ' •. . .· ;, . . ,'. ' . • . :--,. •• • '
·. chlor1·de · -, • • - : ·,._ ··: ·.:. _ ,. , ;• • • . · •· . · · . : •.- . . •• ·•
... • •• f ' • •• • • •

: ,. ',,' : :·: ; . :, , . ' r~; •• ' .•<( ' ::.:. ,.:, , :>' • •• ' .•;,: :,:·:-•• : :• '._· ' ·:' '.: ~'. • •• •, . .•
,· - \ ·. HIN~S TO LONG ANSWER TYPE QUESTION.::,~-··-~--.;-:~·-·-~_, ~· ..• · •
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.,. ' •• -:... • • • ,.,.,..,,;,t" • ., • ..,. • • .. . •
• • ' •. • . .•, I • _' ..... • '. ,:"). • i, • "•

!: (a) ,--·,: "iAgCl •: Sunlight -,_) 2Ag +c(;. \, :. • ·, _. ,•_:· :· ;) <' :- ;: '·•. ·. '_·-.:.: ,_
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(b) , c~0: fl O__:. Ca ( H)

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- . (c)·.:·...N.aOH~fiCl_~·NaCI+:~20 __ :- ... _> . .-··_-,: . .. · 1 ;·_·._._ ' : ·. ; : • . ·_'._ .. •• ,-

.. ·.•,·,·,.1·,· .,;·,.,-,,,.~ ........... "1,•,; ...: , . ' ,, .• '• . • ·. ·' :: •. • ." ..
,; • • I , • • • '--: •. ' I • • • • : ~, ,' • • I • •. • •. • • .p • • • • • • : •, -

. (d) • _cµo·.+2HCl(d~l.]--+~U~l2+H29-, :\·._,:_._ ~-.. -~<:: •. .-·_·..... '.. .

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