Hello friends this is the notes of the chapter chemical reactions and equations . I hope this will help you in your examinations Stay safe, Stay home, Stay connected

2.  PHISICAL CHANGE
 Only phisical
properties are changed
 Eg : Boiling of water,
tearing of paper etc
 Genrally reversable
 No new substance is
formed
 CHEMICAL CHANGE
 Chemical properties are
also changed
 Burning of wood,
curdling of milk etc
 Irreversable
 New substance is
formed

3.  Change in state
 Formation of precipitation
 Evolution of gas
 Change in temperature
 Change in colour

4.  It should represent a true chemical change
 It should be balanced
 It should be molecular
 It should represent the change in
temperature

5.  Basic skeletal eqution
 Writing proper chemical equations
 Balanced chemical equation also called “Law
of conservation of mass”

6.  Write the correct skeletal equation containing
chemical formulae of each reactant and
product
Eg : Reaction of combustion of Benzeen
C6H6 + O2 CO2 + H2O
benzeen + oxygen carbon dioxide + water

7.  Start balancing with the compound that has
maximum number or maximum kind of atoms
 Then balance the element that appear only once on
each side if any . After this balance other elements
 Elementary substances are balanced at the end
 C6H6 + 15/2 O2 6CO2 + 3H2O------(1)
 multiplying equ. (1) by 2 to make equ. (2)
 If all coefficients of reactants or products are not
whole number then multiply whole equation with a
suitable number in order to make all the coefficient
whole number
 2C6H6 + 15O2 12CO2 + 6H2O ------(2)

8.  A chemical reaction involves the breaking of old
bonds and formation of new bonds between
atoms to produce new substances. On the basis
of the nature of bond breaking or bond formation,
Chemical reactions can be mainly classified into
four types as :
(1) Combination reaction
(2) Decomposition reaction
(3) Displacement reaction
(4) Double displacement reaction

9.  Polymerisation reaction
 Exothermic reaction
 Endothermic reaction
 Precipitation reaction
 Neutralization reaction
 Oxidation reaction
 Reduction reaction

10.  The reaction in which two or more reactants
combine to form a single product is known as the
combination reaction
 Example : (1) 2Mg(s) + O2(g) ---- 2MgO(s) + heat
› (2) C(s) + O2(g) ---- CO2(g) + heat
› (3) CaO(s) + H2O(l) ---- Ca(OH)2(aq) + heat

11.  In such reaction, A single reactant breaks
down to give simpler products
 Examples : When CalciumCarbonate is
heated it breaks down into calcium oxide and
carbon dioxide
CaCO3(s) CaO(s) + CO2(g)

12.  Thermal decomposition : when decomposition is
carried out by heating , it is known as thermal
decomposition reaction
 Photochemical decomposition : When the
decomposition reaction is carried out in the
presence of sunlight, It is known as photochemical
decomposition reaction
 Electrolytic decomposition : If the electric current
is used to carry out decomposition reaction. It is
called electrolytic decomposition reaction

13.  In this reaction, a more reactive element displaces
a less reactive element from its compound
 When an iron nail is placed in the blue coloured
aqueous solution of copper sulphate, after some
time we see that iron has displaced the copper
and became iron sulphate and copper was
setteled down at the bottom and then we see that
iron nail became brownish in colour due to
deposition of copper
 Fe(s) + CuSO4(aq) ------FeSO4(aq) + Cu(s)
 In this reaction iron was more reactive than
copper so it displaced copper from copper
sulphate.

14.  In this type of reaction two compounds
reacts by exchange of ions to form two new
compounds. In these relations generally
precipitation occurs
 On mixing silver nitrate solution with sodium
chloride solution, a white precipitate of AgCl
is formed.
 AgNO3(aq) + NaCl(aq) ------ AgCl +
NaNO3(aq)

15.  The process in which a large no. of simple small
molecules are combined together to form very
large molecule is termed as polymerisation
 Example : nCH2 = CH2 ---- ( CH2 – CH2 ) n

16.  In this reaction heat is released along with the
formation of products. In this reaction energy of
reactant is more than that of product.
 Energy of reactant(s) >Energy of product
 Eg. : combustion of methane
 CH4(g) + 2O2(g) ---- 6CO2(aq) + 6H2O(l) +heat +
light
 The production of heat and light are essential
products of combustion while, The presence of
oxygen and combustible substance are essential
conditions for combustion.

17.  Respiration : during digestion, the food is broken
down to form glucose. Glucose then combines
with oxygen in the cells of our body and provides
energy. This reaction or process is called
respiration
 C6H12O6(aq) + 6O2(g) ---- 6CO2(aq) + 6H2O(l) +
energy
 The decomposition of vegetable matter into
compost is an example of exothermic reaction

18.  In this reaction energy is obserbed by the
reactants to complete the reaction. In this reaction
energy of reactant are less than that of product
 Energy of reactant(s) < Energy of product(s)
 Example : decomposition reactions require energy
for breaking down the reactants. Therefore, these
are endothermic reactions
 Decomposition of silver bromide
2AgBr(s) -------- 2Ag(s) + Br2(g)

19.  The reaction in which an insoluble substance
formed, Is called a precipitation reaction and the
insoluble substance is called precipitate
 NaCl(aq) + AgNO3(aq) ---- NaNO3(aq) + AgCl(s)

20.  The reaction in which acid reacts with bases to
form salt and water essentially in dilute aqueous
solution are known as neutralization reactions
 Acid + base ------ salt + water + heat
 Example : HCl(aq) + NaOH(aq) ---- NaCl(aq) +
H2O(l)
 Neutralization reaction is exothermic reaction as
well as double displacement reaction.
 Acid + Base ---- Salt + Water + Energy

21.  Oxidation : loss of electrons from an element or
increase in positive electrovalency of an element
is called oxidation
 E.g : Na ---- Na+ + e- (oxidation)
 Reduction : gain of electrons or increase in
electrovalency of an element is called reduction
 E.g : Cl + e-(reduction)

22.  Oxidising agent : any substance which adds
oxygen, removes hydrogen or removes
electrons from other substance is known as
oxidising agent. It gets reduced in a chemical
reaction
 Reducing agent : any substance which
removes oxygen, adds hydrogen or adds
electrons from other substance is known as
reducing agent. It gets oxidised in a reaction

23.  RED ------ Reduction REDOX
Ox ------ Oxidation
The reaction in which the reduction and oxidation
processes takes place simultaneously are known
as redox reaction
Any redox reaction have two half reactions :
(1) Oxidation half reaction
(2) Reduction half reaction
E.g : Zn + 2H+ -------- Zn2+ + H2

24.  Corrosion :
› The degradation of metal by the action of air, moisture
or a chemical on there surfaces is called corrosion. The
chemical process involved in it is oxidadion
› E.g : Rusting of iron
› 2Fe(s) + 3/2O2(g) + xH2O(l) ---- Fe2O3 . xH2O
› Where x = no. of water molecules

25.  By painting the iron
 By greezing or oiling of iron
 By galvanisation
 By tin-plating and chromium-painting on iron
 By alloying of iron

26.  Food material containing fat or oil when left for a
long time become rancide i.e smell and taste
changes this is because they get oxidised when
they come in contact whith the atmospheric oxygen
 In order to prevent oxidation, some antioxidants like
BHA(Butylated hydroxyanisole), BHT(Butylated
hydroxytoluene), Sodium benzoate etc. are added
to oily and fatty food stuffs. Also keeping food in air
tight container slows down the process of oxidation.
To prevent oxidation chips manufacturers usually
flush the bags of chips with nitrogen gas.
 Rancidity can also be prevented by keeping the
food in as refrigerator or by keeping food away from
sunlight