Question

Place these hydrocarbons in order of decreasing boiling point. Compound Structure butane CH3CH2CH2CH3 pentane CH3CH2CH2CH2CH3 2,2-dimethylpropane CH3 | CH3−C−CH3 | CH3 hexadecane CH3(CH2)14CH3 paraffin

Answer 1

Answer:

Order of hydrocarbons in decreasing order of boiling point:

Paraffin > Hexadecane > Pentane >  Dimethylpropane > Butane

Explanation:

Boiling points of hydrocarbons depend upon:

Mass of the hydrocarbon

Intermolecular forces of interaction

Hydrocarbons of greater mass or greater number of carbons have greater molecular mass.

Molecular formula of paraffin is $CH_3(CH2)_{33}CH3$

Molecular formula of hexadecane is $CH_3(CH2)_{14}CH3$

Among given hydrocarbons, number of carbon is highest in paraffin and hence has highest boiling point.

Boiling point of paraffin is followed by hexadecane having second highest number of carbon.

Mass of dimethylpropane and pentane are comparable. But boiling point of dimethylpropane is less than pentane. This is because branching decreases intermolecular force of attraction (van der Waal's force) which leads to decrease in boiling point.

No. of carbon in butane is least among given. So its boiling point is lowest.

Hence, Order of hydrocarbons in decreasing order of boiling point:

Paraffin > Hexadecane > Pentane >  Dimethylpropane > Butane