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Chemical Reactions and Equations

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Types Of Chemical Reaction

Combination Reaction: The reaction in which two or more reactant combine to form a single product. For example,

  1. Burning of coal
    C (s) + O2 (g) → CO2 (g)
  2.  Formation of water
    2H2 (g) + O2 (g) → 2H2O (l)
  3. CaO (s) + H2O (l) → Ca(OH)2 (aq)

Exothermic Reactions: Reaction in which heat is released along with the formation of products is known as an exothermic reaction.

For example,

  1. Burning of natural gas
    CH4 (g) + O2 (g) → CO2 (g) + 2H2O (g) + Heat
  2. Respiration is also an exothermic reaction.
    C6H12O6 (aq) + 6O2 (g) → 6CO2 (aq) + 6H2O (l) + energy

Combination Reaction

Combination Reaction: The reaction in which two or more reactant combine to form a single product. For example,

  1. Burning of coal
    C (s) + O2 (g) → CO2 (g)
  2.  Formation of water
    2H2 (g) + O2 (g) → 2H2O (l)
  3. CaO (s) + H2O (l) → Ca(OH)2 (aq)

Exothermic Reactions: Reaction in which heat is released along with the formation of products is known as an exothermic reaction.

For example,

  1. Burning of natural gas
    CH4 (g) + O2 (g) → CO2 (g) + 2H2O (g) + Heat
  2. Respiration is also an exothermic reaction.
    C6H12O6 (aq) + 6O2 (g) → 6CO2 (aq) + 6H2O (l) + energy

Decompostion reaction

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.

space left parenthesis straight i right parenthesis space stack 2 space FeSO subscript 4 space left parenthesis straight s right parenthesis with Ferrous space sulphate below space rightwards arrow with Heat space on top stack space Fe subscript 2 straight O subscript 3 space left parenthesis straight s right parenthesis space with Ferric space oxide below plus space SO subscript 2 space left parenthesis straight g right parenthesis space plus space SO subscript 3 space left parenthesis straight g right parenthesis
left parenthesis ii right parenthesis space stack CaCO subscript 3 space left parenthesis straight s right parenthesis with Lime space Stone below space rightwards arrow with Heat on top space stack CaO space left parenthesis straight s right parenthesis space plus space CO subscript 2 space left parenthesis straight g right parenthesis with Quick space Lime below

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

2 space straight H subscript 2 straight O space rightwards arrow from Current to Electric of space 2 straight H subscript 2 space plus space straight O subscript 2

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

2 space AgCl space left parenthesis straight s right parenthesis space rightwards arrow with Sunlight on top space 2 space Ag space left parenthesis straight s right parenthesis space plus space Cl subscript 2 space left parenthesis straight g right parenthesis
2 AgBr space left parenthesis straight s right parenthesis space rightwards arrow with Sunlight on top space 2 space Ag space left parenthesis straight s right parenthesis space plus space Br subscript 2 space left parenthesis straight g right parenthesis

Above reaction is used in black & white photography.

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

stack CaCO subscript 3 space left parenthesis straight s right parenthesis space with Limestone below rightwards arrow with Heat on top stack space CaO space left parenthesis straight s right parenthesis space with Quick space Lime below plus space CO subscript 2 space left parenthesis straight g right parenthesis

Displacement Reaction

Displacement Reaction: The chemical reaction 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 blues the colour of CuSO4 changes dirty green colour due to the formation of FeSO4.

Zn + CuSO4 → ZnSO4 + Cu

Zn is more reactive than copper.

Double Displacement Reaction

Double displacement reaction: A reaction in which new compounds are formed by the mutual exchange of ions between two compounds.

stack Na subscript 2 SO subscript 4 space left parenthesis aq right parenthesis with Sodium space Sulphate below space plus stack space BaCl subscript 2 space left parenthesis aq right parenthesis space with Barium space chloride below rightwards arrow with space on top stack space BaSO subscript 4 space left parenthesis straight s right parenthesis space with Barium space sulphate below plus space stack 2 space NaCl space left parenthesis aq right parenthesis with Sodium space chloride below

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

Oxidation and Reduction

Oxidation:

  1. The addition of oxygen to substance.
  2. The removal of hydrogen from a substance.

2 Cu space plus space straight O subscript 2 space rightwards arrow with Heat on top space 2 space CuO
CuO space plus space straight H subscript 2 space rightwards arrow with Heat on top space Cu space plus space straight H subscript 2 straight O

Element or compounds in which oxygen is added or hydrogen is removed are called to be oxidized.

Oxidizing agent: Compounds which can add oxygen or remove hydrogen element are known as oxidizing agents.

For example, when iron reacts with air, it forms iron oxide (rust)

4Fe + 3O2 → 2Fe2O3

Here, oxygen is added to iron, thus, iron is oxidized. Here oxygen is an oxidizing agent.

When cupric oxide reacts with hydrogen, it gives copper and water.

CuO + H2 → Cu + H2O

Here oxygen is removed from copper and oxygen is added to hydrogen. So, cupric oxide is reduced to copper and hydrogen is oxidized to water. Cupric oxide is oxidizing agent and hydrogen is reducing agent.

Reduction :

  1. The addition of hydrogen to substance.
  2. The removal of oxygen from a substance.

In this reaction CuO is reduced to Cu and H2 is oxidized to H2O. So, "oxidation and reduction taking place together is redox reaction".

Types Of Chemical Reaction

Chemical reactions can be classified into following types:

  1. Combination Reaction
  2. Decomposition Reaction
  3. Displacement Reaction
  4. Double Displacement Reaction
  5. Oxidation and Reduction Reaction

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