Question

Alkanes are called paraffins. They undergo substitution reactions with chlorine in the presence of sunlight. Prove this with a suitable example.

Answer 1

Saturated hydrocarbons alkanes are least reactive so they are considered paraffin. However they undergo some chemical changes under suitable conditions which are substitution reactions.

Complete step by step answer:
As we know alkanes are saturated hydrocarbons. They are considered to be least reactive that’s why they are called paraffins. They undergo generally substitution reactions with $C{l_2}$in presence of sunlight.
$C{H_4}\xrightarrow[{hv}]{{C{l_2}}}C{H_3} - Cl + HCl$
$C{H_3} - Cl\xrightarrow[{hv}]{{C{l_2}}}C{H_2}C{l_2} + HCl$
$C{H_2}C{l_2}\xrightarrow[{hv}]{{C{l_2}}}CHC{l_3} + HCl$
$CHC{l_3}\xrightarrow[{hv}]{{C{l_2}}}CC{l_4} + HCl$
It is experimentally noticed that when direct halogenation takes place, alkanes in presence of sunlight hv, all the hydrogens of the alkanes is replaced by a halogen.
We have discussed the example of Methane (behaves like an alkane) earlier in this question. You can refer to that.
In the example of Methane, in the ultraviolet light, methane reacts with halogen molecules that are chlorine (can also react with bromine). In this reaction the hydrogen is replaced by chlorine so a substitution reaction occurred here.

Additional information: Alkane is an acyclic saturated compound. In general, alkanes consist of carbon and hydrogen atoms arranged in tree structure in which all the carbon-carbon bonds are singly bonded. They have a general chemical formula ${C_n}{H_{2n + 2}}$.
The simplest alkane is $C{H_4}$ with $n = 1$and $C{H_4}$ sometimes called the parent molecule. Alkanes can expand very largely, like pentacontane $({C_{50}}{H_{102}})$ or $6 - ethyl - 2 - methyl - 5 - (1 - methylethyl)$octane , an isomer of tetradecane ${C_{14}}{H_{30}}$
In alkane, carbon is $s{p^3}$ hybridised with $4$ sigma bonds and each hydrogen atom is joined to one of the C-atoms. The longest series of linked carbon atoms in a molecule is known as carbon skeleton. The number of carbon atoms is considered as the size of carbon atoms.

Note: Paraffins or alkanes are trace constituents of biological lipids, but alkanes are the most abundant and stable hydrocarbon constituents of terrestrial rocks.