5. • magnesium ribbon burns with a dazzling white flame and
changes into a white powder.
• This powder is magnesium oxide.
• It is formed due to the reaction between magnesium and
oxygen present in the air.magnesium, etc.
Activity 1. 1
11. From the above three activities, we can say that any of
the following observations helps us to determine whether a
chemical reaction has taken place –
• Change in state
• Change in colour
• Evolution of a gas
• Change in temperature.
Conclusion
12. A chemical reaction is a process where the reactant
gets converted into a product which may be under an
influence of a catalyst .
A word-equation shows change of reactants to products
through an arrow placed between them.
What are chemical reactions ?
13. The reactants are written on the left-hand side
(LHS) with a plus sign (+) between them. Similarly,
products are written on the right- hand side (RHS)
with a plus sign (+) between them.
The arrowhead points towards the products,
and shows the direction of the reaction.
What are chemical reactions ?
15. Writing a chemical reaction
A chemical equation represents a chemical reaction. If you
recall formulae of magnesium, oxygen and magnesium
oxide, the above word-equation can be written as –
Mg+O2 →MgO
16. A chemical reaction is identified by any of these 4
factors
Change in state
change in colour
evolution of a gas
Change in temperature.
According to law of conservation of mass matter can
neither be created nor be destroyed in a chemical
reaction.
ANTOINE LAVOISER
INTRODUCED
LAW OF
CONSERVATION OF
MASS
How do we identify a chemical reaction?
17. That is, the total mass of the elements present in the products of
a chemical reaction has to be equal to the total mass of the
elements present in the reactants.
In other words, the number of atoms of each element remains
then same, before and after a chemical reaction. Hence, we
need to balance a skeletal chemical equation
Balancing a chemical reaction
19. To balance a chemical equation, first draw boxes around each
formula. Do not change anything inside the boxes while
balancing the equation.
List the number of atoms of different elements present in the
unbalanced equation
Start balancing with the compound that contains the maximum
number of atoms. It may be a reactant or a product. In that
compound, select the element which has the maximum number
of atoms.
Balancing a chemical reaction
20. Balance the unbalanced atom.
Finally, to check the correctness of the balanced equation, we
count atoms of each element on both sides of the equation.
To make a chemical equation more informative, the physical states of
the reactants and products are mentioned along with their chemical
formulae. The gaseous, liquid, aqueous and solid states of reactants
and products are represented by the notations (g), (l), (aq) and (s),
respectively.
21. The word aqueous (aq) is written if the reactant or product is present as a
solution in water.
45. THERE ARE 5 TYPES OF REACTIONS WE ARE GOING TO STUDY :-
1. COMBINATION REACTIONS
2. DECOMPOSITION REACTION
3. DISPLACEMENT REACTIONS
4. DUBLE DISPLACEMENT REACTIONS
5. REDOX REACTIONS
TYPES OF CHEMICAL REACTIONS
46. When two or more substances (elements or compounds)
combine to form a single product, the reactions are called
combination reactions
A reaction in which a single product is formed from two or
more reactants is known as a combination reaction.
COMBINATION REACTIONS
48. Calcium oxide reacts vigorously with water to produce
slaked lime (calcium hydroxide) releasing a large amount
of heat.
CaO + H2O > Ca(OH)2
Calcium hydroxide reacts slowly with the carbon dioxide in
air to form a thin layer of calcium carbonate on the walls.
Calcium carbonate is formed after two to three days of white
washing and gives a shiny finish to the walls.
It is interesting to note that the chemical formula for marble
is also CaCO3.
COMBINATION REACTIONS
49.
50. Reactions in which heat is released along with the formation of
products are called exothermic chemical reactions.
Burning of natural gas and the decomposition of vegetable matter
into compost are also an example of an exothermic reaction.
51.
52.
53.
54. Endothermic reaction are those reactions in which heat is
absorbed.
During digestion, food is broken down into
simpler substances.
For example, rice, potatoes and bread contain
carbohydrates. These carbohydrates are
broken down to form glucose. This glucose
combines with oxygen in the cells of our body
and provides energy. So Exothermic process S
55.
56. Decomposition reactions
When a product breaks up into its constituent reactants the reaction is termed as
decomposition reaction.
Heat
2FeSO4 (s) >Fe2O3(s) + SO2 (g) + SO3 (g)
In this reaction you can observe that a single reactant breaks down to give
simpler products. This is a decomposition reaction. Ferrous sulphate crystals
(FeSO4, 7H2O) lose water when heated and the colour of the crystals changes. It
then decomposes to ferric oxide (Fe2O3), sulphur dioxide (SO2) and sulphur
trioxide (SO3). Ferric oxide is a solid, while SO2 and SO3 are gases.
Decomposition of calcium carbonate to calcium oxide and carbon dioxide on
heating is an important decomposition reaction used in various industries.
Calcium oxide is called lime or quick lime. It has many uses – one is in the
manufacture of cement. When a decomposition reaction is carried out by heating,
it is called thermal decomposition.
TYPES OF CHEMICAL REACTIONS
57. • Metals are described as chemical elements that readily lose
valence electrons to form positive ions (cations).
Examples: Aluminium, copper, iron, tin, gold.
• Around 90 of the total 118 elements are metals.
Metals
58. The property of metals by which they can be beaten
into thin sheets is called malleability.
Malleability
59. The property of metal by which it can be drawn into wires is
called ductility.
Ductility
60. Metals produce ringing sounds, they are said to be sonorous.
The materials other than metals are not sonorous
Sonorous
61. ● Hard and have a high tensile strength
● Solids at room temperature, except mercury, which is
liquid at room temperature.
● Sonorous
● Good conductors of heat and electricity
● Malleable, i.e., can be beaten into thin sheet
Physical Properties of Metals
62. ● Malleable, i.e., can be beaten into thin sheets
● Ductile, i.e., can be drawn into thin wires
● High melting and boiling points (except Cesium (Cs) and
Gallium (Ga))
● Dense, (except alkali metals). Osmium – highest density
and lithium – least density
● Lustrous
● Silver-grey in colour, (except gold and copper)
Physical Properties of Metals
63. • Non-metals are those elements, which do not exhibit the
properties of metals.
Examples: Carbon, Boron, etc.
Non-Metals
64. • Materials like coal and sulphur are soft and dull
in appearance.
• They break down into a powdery mass on tapping with a
hammer.
• They are not sonorous and are poor conductors of heat and
electricity.bThese materials are called non-metals.
• The examples of non-metals are sulphur, Carbon, oxygen,
phosphorus, etc.
Non-metals
65.
66.
67. • The name of the product formed in the reaction of sulphur
and oxygen is sulphur dioxide gas.
• When sulphur dioxide is dissolved in water sulphurous acid is
formed.
• The reaction can be given as follows:
Sulphur dioxide + Water →Sulphurous acid
SO2 + H2O H2SO4
• The sulphurous acid turns blue litmus paper red.
Generally, oxides of non-metals are acidic in nature.
Reaction of Non-Metals with oxygen.
68.
69.
70.
71.
72.
73.
74. Reaction with Water
You observed that sodium reacts vigorously with water. Some
other metals do not do so.
For example, iron reacts with water slowly.
75.
76.
77.
78. Reactions with Bases
• What does the ‘pop’ sound indicate?
• As before, the ‘pop’ sound indicates the presence of hydrogen
gas.
• Metals react with sodium hydroxide to produce hydrogen gas.
79.
80. • Many non-metals react with bases to form salts.
• Bases are electron donors whereas non-metals are electron
acceptors. Thus, bases donate electrons to non-metals
which readily accepts them and form a salt.
• Reactions of non-metals with bases are complex.
