Welcome to your ultimate guide on Chemical Reactions and Equations for Class 10! This chapter forms the foundation of Chemistry and is packed with important concepts like types of reactions, balancing equations, and real-life examples. Our notes are simplified, exam-focused, and easy to understand. Whether you're preparing for boards or quick revision, these notes have you covered. Let’s break down the chapter into bite-sized, memorable points!
A chemical reaction
Definition: A chemical reaction
is a process in which the original substance(s) loses its nature and identity
and forms new substance(s)
with different properties.
Breaking of the chemical bonds and formation of new chemical bonds is
responsible for the occurrence of a chemical reaction.
ü The substances
which take part in a chemical reaction are called Reactants.
ü The substances
which are formed in a chemical reaction are called Products.
Examples of chemical reaction:
(i) Digestion of food
(ii) Respiration
(iii) Rusting of iron
(iv) Burning of magnesium
ribbon
(v) Formation of curd
A chemical reaction
can be identified by either of the following observations:
ü Change
in State: For instance, a
solid transforming into a gas.
ü Color
Change: when citric acid
reacts with potassium permanganate solution, then the purple colour of
potassium permanganate solution disappears.
ü Gas
Evolution: Observed when
zinc reacts with hydrochloric acid, producing hydrogen gas.
ü Temperature
Variation: the chemical
reaction between barium hydroxide and ammonium chloride to form barium
chloride, ammonia and water is characterized by a change in temperature (which
is fall in temperature). Ye wala activity tumhare book
mein bhi hai page number 10
ü Formation
of Precipitate: when
potassium iodide solution is added to a solution of lead nitrate, then a yellow
precipitate of lead iodide is formed.
Chemical equations
Definition: A chemical equation
is the symbolic representation of a chemical reaction in the form of symbols
and formulae.
ü It is a way to
represent the chemical reaction in a concise and informative way.
For example,
Magnesium + Oxygen → Magnesium oxide
(Reactants) (Product)
This equation is called word
equation.
The word equation
can be written into chemical equation by writing symbols and formulae of the
substance in place
of their name.
2Mg
+ O2 → 2MgO
Writing a
chemical equation
(i) The symbols of elements and
the formulae of reactants are written on the left hand side of the equation,
with a plus (+) sign between them.
(ii) The symbols and formulae
of the products are written on the right hand side of the equation, with a plus
sign (+) between them.
(iii) An arrow sign (→) is put
between the reactants and the products.
(iv) The physical states of the reactants and products are also
mentioned in a chemical equation.
Skeletal chemical equation: A chemical equation which simply represents
the symbols and formulas of reactants and products taking part in the
reaction is known as skeletal chemical equation for a reaction.
For
example: For the burning of Magnesium in the air, Mg + O2 → MgO is the skeletal
equation.
Balanced Equation: The equation in which atoms
of various elements on both sides of a chemical equation are equal in
accordance with the law of conservation of mass.
Also See: Balancing a
Chemical Equation (Short trick)
Types of
Reaction
Endothermic Reaction: Reactions in which energy
is absorbed.
|
No. |
Reaction |
Equation |
|
1 |
Photosynthesis |
6CO₂(aq) + 6H₂O(l) +
energy → C₆H₁₂O₆(aq) + 6O₂(g) |
|
2 |
Decomposition of
calcium carbonate |
CaCO₃(s) + heat →
CaO(s) + CO₂(g) |
|
3 |
Electrolysis of
water |
2H₂O(l) + energy →
2H₂(g) + O₂(g) |
|
4 |
Photodecomposition
of silver chloride |
2AgCl(s) + light →
2Ag(s) + Cl₂(g) |
Exothermic Reaction: Reactions in which heat is
released along with the formation of products are called exothermic chemical
reactions. Some examples are given below
|
No. |
Reaction |
Equation |
|
1 |
Combustion of
methane |
CH₄(g) + 2O₂(g) →
CO₂(g) + 2H₂O(g) + heat |
|
2 |
Neutralization of
acid and base |
HCl(aq) + NaOH(aq) →
NaCl(aq) + H₂O(l) + heat |
|
3 |
Respiration |
C₆H₁₂O₆(aq) + 6O₂(g)
→ 6CO₂(g) + 6H₂O(l) + energy |
|
4 |
Reaction of calcium
oxide with water |
CaO(s) + H₂O(l) →
Ca(OH)₂(aq) + heat |
Combination Reaction: When two or more
substances (elements or compounds) combine to form a single product, the
reactions are called combination reactions
Displacement Reaction: Those reactions in which one element takes the place of another element in a compound, are known as displacement reactions.
ü In
general, a more reactive element displaces a less reactive element from its
compound.
ü Zn + CuSO₄ → ZnSO₄ + Cu
ü This displacement reaction takes place because zinc is more reactive than copper.
Double Displacement Reaction: Those reactions in which two compounds react by an exchange of ions to form two new compounds are called double displacement reactions.
ü A double displacement reaction usually occurs in solution and one of the products, being insoluble, precipitates out (separates as a solid)
ü
BaCl₂ + Na₂SO₄ → BaSO₄ + 2NaCl
ü In
this reaction, barium sulphate is formed as a white, insoluble solid (called
precipitate) which separates out suddenly from the solution.
Decomposition Reaction: Reactions in which a
compound splits up into two or more simpler substances are known as
decomposition reactions.
ü A decomposition reaction is just the opposite
of a combination reaction.
ü
The
decomposition reactions are carried out by applying heat, light or electricity
Oxidation and Reduction Reactions: concept of oxidation and reduction is based on the addition or removal of oxygen or hydrogen elements.
🔥 Oxidation and Reduction – Key Concepts
✅ 1. Oxidation
- Definition: Gain of oxygen or loss of hydrogen.
- Example: Zn → ZnO (Zinc gains oxygen and gets oxidised)
✅ 2. Reduction
- Definition: Loss of oxygen or gain of hydrogen.
- Example: CuO → Cu (Copper loses oxygen and gets reduced)
✅ 3. Oxidising Agent
- Definition: The substance that causes oxidation and itself gets reduced.
- Example: CuO in the reaction
- CuO + H₂ → Cu + H₂O
✅ 4. Reducing Agent
- Definition: The substance that causes reduction and itself gets oxidised.
- Example: H₂ in the reaction
- CuO + H₂ → Cu + H₂O
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