CBSE Class 11 Chemistry Hydrocarbon Notes Set A

 HYDROCARBON

◊ Hydrocarbons are composed of Carbon and hydrogen.

◊ The important fuels like Petrol, kerosene, coal gas, CNG, LPG etc. are all hydrocarbons or their mixture. 

Sources: Petroleum and natural gas are the major sources of aliphatic hydrocarbon while coal is an important source of aromatic hydrocarbons. The oil trapped inside the rocks is known as petroleum. PETRA – ROCK, OLEUM – OIL. The oil in the petroleum field is covered with a gaseous mixture known as natural gas. The main constituents of the natural gas are methane, ethane, propane and butane.

♦ Physical Properties:-

(1) Nature:- Non-Polar due to covalent nature of C—C bond and C—H bond. C— C bond enrgy = 83 kj/mole and C—H bond energy = 99 kj/mole.

C₁—C4 = gases, C₅—C₁₇ = colourless odourless liquid and > C₁₇ = Solid.

(2) Solubility:- Like dissolve like Viz, Polar compounds dissolve in polar solvent and Non-Polar compound dissolve in non polar solvent.

(3) Boiling point:- Low boiling point due to non polar in nature. 

The molecules are held together only by weak Van der Waalls’ forces. Since we known that the magnitude of Van der Waalls’ forces is directly proportional to the molecular size. Therefore, the boiling point increases with increase the molecular size i.e. with increase in number of carbon atoms.
Noted:- the boiling points of the branched chain Alkanes are less than the straight chain isomers.
This is due to the fact that branching of the chain makes the molecule more compact and thereby decreases the surface aria and consequently, the magnitudes of Van der Waalls’ forces also decrease.

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