by Class 10 Science notes are so useful for upcoming CBSE exams for better preparation and concept learning. Chapter 1 is about the basic knowledge of chemical reactions and equations. You will learn the concept of the balancing the equations. Also the types of reactions.
These notes will give you the full chapter learning of Class 10 Science chapter 1.
Class 10 Science notes
CHAPTER -1
Chemical reaction and equations notes
Chemical reactions are the process in which new substance properties are formed.
During a chemical reaction, atoms of one element do not change into those of another element; only a rearrangement of atoms takes place in a chemical reaction.
- The substances which take part in a chemical reaction are called reactants.
- The new substances produced as a result of chemical reactions are
called products.
Ex-
Magnesium +oxygen→(heat)→magnesium oxide
(As ribbon) (From air) (White powder)
More examples-
Souring of milk, formation of curd from milk, cooking of food,
process of respiration, rusting of iron, etc.
Characteristics of chemical reactions:
The easily observable feature which take place as a result of Chemical Reaction
are known as characteristics of Chemical→ Reaction
- Important characteristics are:-
- Change in state
- Change in colour
- Evolution of a gas
- Change in temperature
- Formation of precipitation
Chemical equation
The method of representing a chemical reaction with the help of symbols and
formulae of the substance involved in it is known as a chemical reaction.
Zinc + sulphuric acid → Zinc sulphate + hydrogen
Symbol of zinc→Zn
Formula of sulphuric acid →H₂SO₄
Formula of Zinc sulphate is →ZnSO₄
Formula of Hydrogen is →H₂
Zn + H₂SO₄ → ZnSO₄ + H₂
(reactant) (product)
- The substances which combine or react are known as reactants. Zinc and sulphuric acid are the reactants here.
- The substances produced in a reaction are known as products. Zinc sulphate and hydrogen are products.
- an arrow sign (→) pointing towards the right hand side is put between the reactants and products.
Balancing of chemical equation –
The process of making different types of atoms equal on both sides of an equation
is called balancing of equations.
For example –
Hydrogen burns in oxygen to form water.
This reaction can be written in an equation
H₂+O₂→H₂O
Reactants products
No.of H atom- 2 2
No.of O atom- 2 1
We have to balance ‘O’. we will multiply H₂O by 2 so that
H₂+O₂→2H₂O
Reactants products
No of H atom 2 4
No of O atom 2 2
Now hydrogen (H) becomes unbalanced so we will multiply by 2 in H₂
2H₂+O₂→2H₂O
Reactants products
No of h atom 4 4
No of o atom 2 2
*Balanced chemical equation:
A balanced chemical equation has an equal number of atoms of different elements in the reactants and products .
Zn+ H₂SO₄→ ZnSO₄+ H₂
Reactants products
No of Zn atom: 1 1
No of H atom: 2 2
No of S atom: 1 1
No of O atom: 4 4
So there is an equal number of atoms of different elements in the reactants and
products, so the above equation is a balanced equation.
*so a balanced chemical equation has equal masses of various elements in reactants
and products.
Ex-
H₂+O₂→2H₂O
Reactant products
No of H atom 2 4
No of O atom 2 2
Here no of elements of oxygen is unequal so this equation is called unbalanced chemical equation .
More example-
- Fe+H₂O→ Fe₃O₄ +H₂
Reactant products
No of fe atom 1 3
H atom 2 2
O atom 1 4
Fe+4H₂O→Fe₃O₄+4H₂
Reactant product
O atoms 4 4
H atoms 8 2
3Fe+4H₂O→Fe₃O₄+4H₂
Reactant products
Fe atoms 3 3
O atoms 4 4
H atoms 8 8
- HNO₃+Ca(OH₂) →Ca(NO₃) ₂+H₂O
- NaOH+H₂SO→Na₂SO₄+H₂O
- NaCL+AgNO₃→AgCL +NaNO₃
- BaCL₂+H₂SO→BaSO₄+HCl
Solution:
2) 2HNO₃+Ca(OH₂) →Ca(NO₃) ₂+2H₂O
3) 2NaOH+H₂SO→Na₂SO₄+2H₂O
4)balanced
5)BaCL₂+H₂SO→BaSO₄+2HCl
Writing symbols of physical states
The gaseous , liquid, aqueous and solid states of reactants and products are
represented by the (g)(l)(aq)and (s) respectively
3Fe(s)+4H₂O(g)→Fe₃O₄(s)+4H₂(g)
CO(g)+ 2H₂(g) → CH₃OH(l)
340 atm
sunlight
6CO₂(aq)+12H₂O(l)→C₆H₁₂O₆ (aq)+6O(aq)+6HO(l)
chlorophyll
Photosynthesis reaction-
6CO₂(aq)+12H₂O(l)→C₆H₁₂O₆ (aq)+6O(aq)+6HO(l)
Types of chemical reaction-
1)combination reaction-
A reaction in which a single products is formed from two or more reactant is known as a combination reaction
CaO(s) + H2O(l) → Ca(OH)2
Slaked lime is used for white washing walls calcium hydroxide reacts slowly
with the carbon dioxide in air to form a thin layer of calcium carbonate.
marble↴
Ca(OH)2 (aq) + CO2 → CaCO3 (s) + H2O (l)
(calcium hydroxide) (calcium carbonate)
2)burning of coal-
C(s)+O₂ (g) →CO₂ (g)
3) formation of water from H₂(g) and O₂(g)-
2H₂(g)+O₂(g) →2H₂O(l)+heat
When a large amount of heat is evolved .
This makes the reaction mixture warm . A reaction in which heat is released
along with the formation of products is called an exothermic chemical reaction.
Natural gas →CH4
Other examples of exothermic reaction are :
(i)burning of natural gas
CH4 (g) + 2O2 (g) → CO2 (g) + 2H2O (g) + Heat
(methane)
- (ii)The carbohydrates which we eat are broken down to form glucose.
This glucose combines with oxygen in the cell of our body and provides energy.The name of this reaction is respiration.
(iii)decomposition of vegetable matter is also an exothermic reaction.
2) decomposition reaction:
AB→A+B
A reaction in which a single reactant breaks down to give simpler products.
This is a decomposition reaction
Heat
2FeSO4 → Fe2O3 (s) + SO2 (g) + SO3 (g)
(ferrous sulphate) (ferric oxide)
Heat
CaCO3(s) → CaO(s) +CO2 (g)
(limestone) (quick lime)
Heat
Pb(NO3)2 → 2PbO (s) + 4NO2 (g) + O2 (g)
(lead nitrate) (lead oxide) (nitrogen dioxide) (oxygen)
A reaction which requires energy either in the form of heat, light.
Or electricity for breaking down the reactants.
Such reactions in which energy is absorbed are known as endothermic reactions
sunlight
2AgCl (s) → 2Ag(s) + Cl2 (g)
(ferrous sulphate) (ferric oxide)
3)displacement reaction
A reaction in which a substance displaced or removed another element. This The reaction is known as displacement reaction
Fe(s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
(copper sulphate) (iron sulphate)
Zn(s) + CuSO4 (aq) → ZnSO4 (aq) + Cu (s)
(copper sulphate) (zinc sulphate)
4)double displacement reaction-
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
PbNO2 + KI → PbI2 + KNO2
5)oxidation and reduction-
If a substance gains oxygen during a reaction it is said to be oxidized.
If a substance loses oxygen during a reaction it is said to be reduced.
Heat
2Cu + O2 → 2CuO
Heat
CuO + H2 → Cu + H2O
A reaction ,in which one reactant is oxidized while other gets reduced during
a reaction, such reactions are called oxidation-reduction or redox reactions.
⬇_______oxidation_____⬇
CuO + H2 → H2O + Cu
⬇_______reduction_____⬆
ZnO + C → Zn + CO
MnO2 + 4HCl → MnCl2 + 2H2O + Cl2
Corrosion-
When a metal is attacked by substances around it such as moisture ,acid etc. it is said to corrode and this process is corrosion.
The black coating on silver and green coating on copper are examples of corrosion.
Rancidity –
Spoilage of food in such a way that it becomes undesirable
(and usually unsafe) for consumption.
- *When fats and oils are oxides, they become rancid and their smell and
taste changes.
- *Usually substances which prevent oxidation (antioxidation )are added to food containing fats and oils.
IMPORTANT QUESTIONS
(1)why cannot a chemical change be normally reversed?
(2)why should a magnesium ribbon be cleaned before burning in air?
(3)why do we apply points on iron articles?
(4)oils and fats containing food items are flushed with nitrogen why?
(5)what happens chemically when quick lime is added to water?
(6)why respiration is considered an exothermic reaction?
(7)with the help of an activity show that iron is more reactive than copper?
(8)why does the colour of copper sulphate solution change when an iron nail is
dipped in it?
(9)What is an exothermic and endothermic reaction ?Give examples.
So we hope, You got the accurate notes for the class 10 science preparations. Also check notes of the chapters of the class 10 science ncert book.
