TYPES OF CHEMICAL REACTIONS - 12th class Science

 TYPES OF CHEMICAL REACTIONS - 12th class Science

(1)COMBINATION REACTION: The reaction in which two or more reactant combine to form a single product. 

 e.g. (1) Burning of coal

C(s) + O₂(g) → CO₂(g)

 (2) Formation of water

2H₂ (g) + O₂(g) → 2H₂0 (1)

(3) CaO(s) + H₂0 (1)→Ca(OH)₂(aq)

    Quick lime                Slaked lime

Exothermic Reacions: Reaction in which heat is released along with formation of products.

 e.g., (i) Burning of natural gas.

CH₄(g) + O₂ (g)→ CO₂ (g) + 2H₂O(g) + Heat 

(ü) Respiration is also an exothermic reaction.

C₆H₁₂O₆(aq) + 6O₂(g) → 6CO₂(aq) + 6H₂O (1) + energy 

(2). DECOMPOSITION REACTION: The reaction in which a compound splits into two or more simple substances  is called decomposition reaction.

                                                            A→ B+C 

• Thermal decomposition : When decomposition is carried out by heating. 

             Eg: (1) 2FeSO₄ (s) →Heat > Fe₂O₃(s) + SO₂(g) + SO₃ (g)

                    (Ferrous sulphate)          (Ferric oxide)

                    Green colour                Red-brown colour 

          (2) CaCO₃ (s) →(Heat)CaO (s) + CO₂ (g)

              (Lime stone)     (Quick lime)

•  Electrolytic Decomposition: When decomposition is carried out by passing electricity.

            Eg: (1)2H₂0 (electric current) → 2H₂ + O₂

•  Photolytic Decomposition: When decomposition is carried out in presence of sunlight. 

              e.g., (i) 2AgCl (s) (sunlight) → 2Ag (s) + Cl₂(g)

                       2AgBr (s) (Sunlight) → 2Ag (s) + Br₂ (g)

 Above reaction is used in black and white photography.

• Endothermic Reaction: The reactions which require energy in the form of heat, light or electricity to  break reactants are called endothermic reactions. 

(3)DISPLACEMENT REACTION: The chemical reactions in which more reactive element displaces less reactive element from its salt solution. 

Fe (s)+ CuSO₄(aq) → FeSO₄ (aq) + Cu (s)

The iron nail becomes brownish in colour by deposition of Cu and blue colour of CuSO₄ changes dirty green clour due to formation of FeSO₄. 

Zn + CuSO₄ + ZnSO₄ + Cu

Zn more reactive than copper.

 (4) DOUBLE DISPLACEMENT REACTION: A reaction in which new compounds are formed by

mutual exchange of ions between two compounds.

Na₂SO₄ (aq) + BaCl₂ (aq) → BaSO₄ (s) + 2NaCl (aq)

                                (Sodium sulphate)  +  (Barium chloride) → (Barium sulphate) + (Sodium chloride) 

      White precipitate of BaSO₄ is formed, so it is also called precipitation reaction. 

(5)OXIDATION AND REDUCTION: 

Oxidation : It is a process of gaining oxygen during a reaction.

 2Cu + O₂ (Heat) → 2CuO

 CuO + H2(Heat) → Cu + H₂O 

Reduction : Reduction is just reverse of oxidation. It is a process of losing oxygen during a reaction.

                         CuO + H₂ → Cu + H₂O 

In this reaction CuO is reduced to Cu and H₂ is oxidized H₂O. In other words, one reactant gets oxidised while the other gets reduced. Such reactions are called oxidation-reduction reactions or redox reactions. 

Seven Primitive Unit Cells and their Possible Variations as Centred Unit Cells - 12th class

Seven Primitive Unit Cells and their Possible Variations as Centred Unit Cells - 12th class chemistry

Crystal system	Possible variations	Axial distances or edge lengths	Axial angles	Examples
Cubic	Primitive, Body-centred, Face-centred	a= b = c	𝝰 = 𝝱 = γ = 90°	NaCl, Zinc blende, Cu
Tetragonal	Primitive, Body-centred	a = b  ≠ c	𝝰 = 𝝱 = γ = 90°	White tin, SnO₂,TiO₂, CaSO₄
Orthorhombic	Primitive, Body-centred, Face-centred, End-centred	a ≠  b  ≠ c	𝝰 = 𝝱 = γ = 90°	Rhombic sulphur, KNO₃, BaSO₄
Hexagonal	Primitive	a = b  ≠ c	𝝰 = 𝝱 = 90° γ =120°	Graphite, ZnO, CdS
Rhombohedral or Trigonal	Primitive	a= b = c	𝝰 = 𝝱 = γ ≠ 90°	Calcite(CaCO₃), HgS (cinnabar)
Monoclinic	Primitive, End-centred	a ≠  b  ≠ c	𝝰 = γ = 90° 𝝱  ≠ 90°	Monoclinic sulphur, Na₂SO₄.10H₂O
Triclinic	Primitive	a ≠  b  ≠ c	𝝰 ≠ 𝝱  ≠ γ ≠ 90°	K₂Cr₂O₇, CuSO₄, 5H₂O,H₃BO₃

Different Types of Solids - 12th class chemistry

Different Types of Solids - 12th class chemistry

Type of Solid	Constituent Particles	Bonding/ Attractive Forces	Examples	Physical Nature	Electrical Conductivity	Melting Point
(1) Molecular solids (i) Non polar (ii) Polar (iii) Hydrogen bonded	Molecules	Dispersion or London forces Dipole-dipole interactions Hydrogen bonding	Ar,CCl₄, H₂,I₂,CO₂ HCl, SO₂ H₂O(ice)	Soft Soft Hard	Insulator Insulator Insulator	Very low Low Low
(2) Ionic solids	Ions	Coulombic or electrostatic	NaCl, MgO, ZnS, CaF₂	Hard but brittle	Insulators in solid state but conductors in molten state and in aqueous solutions	High
(3) Metallic solids	Positive ions in a sea of delocalised electrons	Metallic bonding	Fe, Cu, Ag, Mg	Hard but malleable and ductile	Conductors in solid state as well as in molten state	Fairly high
(4) Covalent or network solids	Atoms	Covalent bonding	SiO₂(quartz), SiC, C(diamond), AIN, C (graphite)	Hard Soft	Insulators Conductor (exception)	Very  high

Distinction between Crystalline and Amorphous Solids - 12th Chemistry

Distinction between Crystalline and Amorphous Solids - 12th Chemistry

Property	Crystalline solids	Amorphous solids
Shape	Definite characteristic geometrical shape	Irregular shape
Melting point	Melt at a sharp and characteristic temperature	Gradually soften over a range of temperature
Cleavage property	When cut with a sharp edged tool, they split into two pieces  and the newly generated surfaces are plain and smooth	When cut with a sharp edged tool, they  cut into two pieces with irregular surfaces
Heat of fusion	They have a definite and characteristic enthalpy of fusion	They do not have definite enthalpy of fusion
Anisotropy	Anisotropic in nature	Isotropic in nature
Nature	True solids	Pseudo solids or super cooled liquids
Order in  arrangement of constituent particles	Long range order	Only short range order.