Chemical Reaction and Equation: Short Notes

The short notes for the chapter Chemical Reaction and Equation are as follows:

• Chemical Equation

The representation of chemical reaction by means of symbols of substances in the form of formulae is called chemical equation.
For example N₂ + 3H₂ ⇌ 2NH₃

• Balanced Chemical Equation

A balanced chemical equation has equal number of atom of each element participating in the reaction on both left and right hand sides of the reaction.
According to Law of Conservation of Mass, total mass of the elements present in the products of a chemical reaction has to be equal to the total mass of the element present in the reactants.

• Balancing Of A Chemical Equation

Total No of Atoms on R.H.S = Total no of Atoms on L.H.S.
Fe₃O₄ + H₂ → Fe + H₂O
[Fe] Fe₃O₄ + H₂ → 3Fe + H₂O
[O] Fe₃O₄ + H₂ → 3Fe + 4H₂O
[H] Fe₃O₄ + 4H₂ → 3Fe + 4H₂O

• Types Of Chemical Reactions

The transformation of chemical substance into a new chemical substance by making and breaking of bonds between different atom is known a chemical reaction.

(i) Combination Reaction: When two elements or one compound and one element or two compounds combine to form a new product.
Foi example
• H₂ + Cl₂ → 2HCl
• Zn + CuSO₄ → ZnSO₄ + Cu
• NaOH + H₂SO₄ → Na₂SO₄ + H₂O

(ii) Decomposition Reaction: When a compound-split into two or more simple products for example

Decomposition reaction require energy either in the form of heat, light or electricity for decomposing the reactions.

(iii) Displacement Reactions: It takes place when a more reactive metal displaces a less reactive metal. For Example:
Fe + CuSO₄ → FeSO₄ + Cu

(iv) Double Displacement Reactions: In this reactions ions are exchanged between two reactants and forming new compounds.

• Other types of chemical reactions

(i) Exothermic Reactions: Reactions producing energy are called exothermic reactions.
Most of the combination reactions are exothermic in nature.
For example : CaO + H₂O → Ca(OH)₂ + Heat

(ii) Endothermic Reactions: Reactions which require energy to occur are known as endothermic reactions.
For example: 

(iii) Oxidation: Gain of oxygen or removal of hydrogen is called oxidation eg.
• Zn + O₂ → ZnO
• Mn + HCl → MnCl₂ + H₂

(iv) Reduction: Gain of hydrogen or removal of oxygen is called reduction.
e.g. CuO + H₂ → Cu + H₂O

(v) Redox Reactions: A chemical reaction in which both oxidation and reduction takes place simultaneously are called redox reactions.
e.g., CuO + H₂ → Cu + H₂O

(vi) Precipitation Reaction: In some reactions, an insoluble mass is formed which is known as precipitate and such reactions are called precipitation reaction.
For Example
Na₂SO₄ + BaCl₂ → 2NaCl + BaSO₄ (White ppt.)

• Oxidation In Everyday Life

(i) Rusting: When iron reacts with oxygen and moisture it forms a red substance called rust.

(ii) Corrosion: Metals on coming in contact with oxygen, water, acids or gases presents in air changes its surface. This is called corrosion for e.g. black coating on silver and green coating on copper.
Prevention – painting, galvanization, oiling, greasing

(iii) Rancidity: Oil and fats on exposure to air show a change in taste and smell. This property is known as rancidity.
Prevention – adding antioxidants, vacuum packing, refrigeration, flushing food with nitrogen.

• Chemically rust is hydrated ferric oxide, i.e., Fe₂O₃.xH₂O

To understand the whole chapter, watch:

If you are facing problem in identifying oxidising and reducing agent, watch this to clear your confusion.

Read More: 64 Q&A of Chemical Reactions and Equations including NCERT

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