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Properties of alkanes (Grade 10 Students)

Properties of Alkanes

Physical Properties 

Alkanes containing four carbon atoms (i.e. methane, ethane, propane and butane) are colorless, odorless gases. Alkanes containing five to seventeen carbons atoms are colorless , odorless liquids. Higher alkanes are also colorless, odorless solids.

Chemical Properties

Halogenation of Alkanes

A reaction in which a hydrogen of alkane is replaced by a halogen atom is called halogenation. 

In diffused Sunlight

Halogenation takes place in the presence of diffused sunlight. 

If halogen is present large quantity, this reaction continues to take place as follows.
The chlorination of methane usually produce a mixture of products. 
In Direct Sun light
Reaction of methane with chlorine in direct sunlight is explosive and gives carbon and HCl.
The halogens react with alkane with following reactivity order: F2 > Cl2 > Br2 > I2. Fluorine reacts explosive; Chlorine reacts slowly in dark at room temperature but rapidly in strong sunlight. Bromine is less reactive than chlorine and requires high temperature or strong sunlight. Iodine is essentially unreactive. 

2. Combustion

A reaction in which a substance reacts with oxygen (air) and produces instant heat and flame along with products is called combustion.  

Complete combustion of an alkane produces carbon monoxide, water and heat. Most of alkane burn with blue flame.


Incomplete combustion occurs in the presence of limited supply of oxygen. Incomplete combustion of methane gives CO, C and H2O.


Uses  of methane
Methane is useds as
a. as domestic fuel (sui gas)
b. as a fuel for automobile (CNG)
c. to manufacture urea fertilizers.
Question. Why lighter alkanes are widely used as fuel?
Answer. 
Lighter alkanes are widly used as fuel because:
i. Their combustion can be controlled.
ii. They produce large amount of heat per gram
iii. They are cheap and readily available.
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