Balance the following chemical equation and identify the type of reaction they
represent
KClO3 ¾¾® KCl + O2
NH3 + O2 ¾¾® NO + H2O
Na2O + H2O ¾¾® NaOH
Na + H2O ¾¾® NaOH + H2
FeCl3 + NaOH ¾¾® Fe (OH)3 + NaCl.
Answers
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3 X – Science
CHAPTER – 1
q Chemical Reaction : –Whenever a chemical change occurs we can say that
a chemical reaction has taken place
eg – Food gets digested in our body
– Rusting of iron.
q Chemical Equation :–Achemical reaction can be expressed symbolically
by using chemical equation
eg magnesium is burnt into air to form magnesium oxide can be represented
as
Mg + O2 ®MgO
– We can observe or recognise a chemical reaction by observing change
in state, colour, by evolution of gas or by change in temperature.
q Physical state of the reactant and products are mentioned to make chemical
reaction more informative. eg we use (g) for gas, (l) for liquid, (s) for solid
and (aq) for aqueous.
q Balancing Equation :– We balance the chemical equation so that no. of
atoms of each element involved in the reaction remain same at the reactant
and product side.
eg Fe + H2O ® Fe2O3 + H2 can be written as
3 Fe(s) + 4H2O(g) ® Fe2O3(s) +4H2(g)
q Combination Reaction :– The reaction in which two or more substances
combine to form a new single substance
ChemicalReactionsandEquations
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4 X – Science
eg CaO(s) + H2O(l) ¾¾® Ca(OH)2 (aq)
Calcium Water Calciumhydroxide
oxide (slaked lime)
Quick lime
– Ca(OH)2 slaked lime is used for white washing walls. It reacts will CO2 to
form CaCO3 and gives a shiny finish to the walls.
Ca(OH)2(aq)+ CO2(g)
¾¾® CaCO3(s)+ H2O (l)
Calcium Calcium
hydroxide Carbonate
– Burning of Coal
C(s) + O2(g) ¾¾® CO2(g) + heat + light
– Formation of water
2H2(g) + O2(g) ¾¾® 2H2O(l)
q Exothermic Reactions :– Reaction in which heat is released along with the
formation of products.
eg. CH4(g) + 2O2(g) ¾¾®CO2(g) + 2H2O(g)
– Respiration is also exothermic reaction.
– De composition of vegetable matter into compost.
q De compositon Reactions :– The reaction in which a single substance
decomposes to give two or more substances. De composition reactions can
be of three types
Thermal Decompositon :–When a decompositon reaction is carried out by
heating
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5 X – Science
– Silver bromide behaves similarly
2Ag Br ¾¾Su¾nl¾igh¾t¾® 2Ag(s) + Br2(g)
– The above two reactions are used in black and white photography.
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6 X – Science
– Endothermic Reactions – The reactions which require energy in the form
of heat, light or electricty are called Endothermic Reactions.
2Ba(OH)2 + NH4Cl ¾¾® 2BaCl2 + NH4OH
– Displacement Reaction : The chemical Reaction in which an element
displaces another element from its solution
Fe(s) + CuSO4(aq) ¾¾® FeSO4 + Cu(s)
Copper (aq)
Sulphate Iron Sulphate
– The nail becomes brownish in colour and the blue colour of Copper Sulphate
solution fade.
– Other examples Zn(s) + CuSO4 ¾¾® ZnSO4 + Cu(s)
(aq) (aq)
Copper Zinc
Sulphate Sulphate
Pb(s) + CuCl2 ¾¾® PbCl2 + Cu(s)
(aq) (aq)
Copper Lead
Chloride Chloride
– Zinc and lead are more reactive elements than copper. They displace copper
from its compounds.
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7 X – Science
– Double Displacement Reaction : The reaction in which two different atoms
or group of atoms are mutually exchanged
eg. Na2 SO4 + BaCl2 ¾¾® BaSO4(s) + 2NaCl
(aq) (aq) (aq)
Sodium Barium Barium Sodium
Sulphate Chloride Sulphate Chloride
A white substance is formed due to above reaction. The insoluble substance
is called precipitate.
Precipitation Reaction –Any reaction that produces a precipitate is called a
precipitation reaction.
eg. Pb(NO3)2 + 2KI ¾¾® PbI2 +2KNO3
(aq) (aq) (aq)
Lead Nitrate Potassium Lead Potassium
Iodide Iodide Nitrate
– Oxidation : Oxidation is the gain of oxygen or loss of hydrogen
eg. 2Cu + O2 ¾¾He¾at¾® 2CuO
When Copper is heated a black colour appears. If this CuO is reacted with
hydrogen gas then again Cu becomes brown as reverse reaction takes place
CuO + H2 ¾¾He¾at¾® Cu + H2O
– Reduction : Reduction is the loss of oxygen or gain of hydrogen.
– Redox Reaction : The reaction in which one reactant gets oxidised while
other gets reduced
eg. ZnO + C ¾¾® Zn + CO
MnO2 + 4HCl ¾¾® MnCl2 + 2H2O + Cl2
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8 X – Science
– Corrosion : When a metal is attacked by substances around it such as
moisture, acids etc.
eg. Reddish brown coating on iron.
(ii) Black coating on Silver.
– Rancidity : When fats and oils are oxidised they become rancid and their
smell and taste change.
– Antioxidants are added to foods containing fats and oil.
Answer:
1.) 2KClO3 --------->2 KCl + 3O2 =====>>> Decomposition Reaction
2.) 4NH3 + 5O2 ------> 4NO + 6H2O ====>>> Oxidation Reaction
3.) Na2O + H2O --------> 2NaOH =====>>> Combination Reaction
4.)2 Na + 2 H2O -------------> 2NaOH + H2 ====>>> Single displacement reaction
5.) FeCl3 +3NaOH ----------> Fe(OH)3 + 3NaCl =====>>> Double Displacement reaction