Class 10 – : Chemical Reactions and Equations notes: –

Chemical reactions: –

The transformation of chemical substance into a new chemical substance by making and breaking of bonds between different atoms is known as Chemical Reaction.

Signs of a chemical reaction: –

These factors denote that a chemical reaction has taken place- change of state of substance, change of color of substance, evolution of heat, absorption of heat, evolution of gas and evolution of light.

Chemical Equation: –

The representation of chemical reaction by means of symbols of substances in the form of formulae is called chemical equation. E.g.

2H₂ + O₂ —————–> 2H₂O

Balanced Chemical Equation: –

A balanced chemical equation has number atoms of each element equal on both left and right sides of the reaction.

*Note- According to Law of Conservation of Mass, mass can neither be created nor destroyed in a chemical reaction.

To obey this law, the total mass of elements present in reactants must be equal to the total mass of elements present in products.

Types of Chemical Reactionshttps://www.youtube.com/embed/Rka7s9oLzd4?version=3&rel=1&fs=1&autohide=2&showsearch=0&showinfo=1&iv_load_policy=1&wmode=transparent

1) Combination Reaction or Addition Reaction: –

When two elements or one element and one compound or two compounds combines to give one single product.

A + B ————> AB

Eg.              H₂ + Cl₂ ————-> 2HCl

2) Decomposition: –

Splitting of a compound into two or more simple products.

ABC ————-> AB + C

Eg.              CaCO₃ ——Δ——–> CaO + CO₂

3) Displacement: –

It takes place when a more reactive metal displaces a less reactive metal.

AB + C —————> AC + B

Eg.              CuSO₄ + Zn ————-> ZnSO₄ + Cu

4) Double displacement: –

Reactions in which ions are exchanged between two reactants forming new compounds are called double displacement reactions.

AB + CD ————-> AC + BD

Eg.    CaCl₂ + Na₂SO₄ ————-> CaSO₄ + 2NaCl

5) Precipitation: –

The reaction in which an insoluble compound called precipitate form is called precipitation reaction.

Eg.              (NH₄)₂SO₄ + BaCl₂ ———> BaSO₄ (white ppt) + 2NH₄Cl

6) Exothermic: –

Reactions which produce energy are called exothermic reaction. Most of the decomposition reactions are exothermic.

A ———–> B                -∆H

Eg.    CH₄ + O₂ —————> 2CO₂ + H₂O + heat

7) Endothermic: –

Reactions which absorb energy are called endothermic reaction. Most of the combination reactions are endothermic.

A ————–> B            +∆H

Eg.    6CO₂ + 6H₂O + heat ———–> C₆H₁₂O₆ + 6O₂

8) Oxidation: –

Increasement in the oxidation number is known as oxidation.

Eg. (a) Addition of oxygen or any electronegative element.

(b) Removal of hydrogen or any electropositive element.

(c) Removal of electron

Note: Oxidation no. is a range varies from valency to valance electron of the element.

9) Reduction: –

Decreasement in the oxidation number is called reduction.

Eg. (a) Removal of oxygen or any electronegative element.

(b) Addition of hydrogen or any electropositive element.

(c) Addition of electron.

10) Redox: –

A chemical reaction where oxidation and reduction both take place simultaneously are also known as redox reaction.

Eg.              2FeCl₃ + SnCl₂ ————> 2FeCl₂ + SnCl₄

Rusting: –

Formation of oxide layer on the surface of metal due to presence of air and moisture is called rusting.

Corrosion: –

Destruction of metal due to formation of oxide layer on its surface is called corrosion.

Rancidity: –

Oxidation of oil and fats on exposure to air leads to change in taste and smell is known as rancidity.