Alkanes - Physical Properties and its Uses

Alkanes are a homologous series of hydrocarbons.

Alkanes can be represented by a general chemical formula.

This represents that all alkanes have a similar functional group.

Because they are a homologous series, alkanes exhibit gradual trends in its physical properties.

Now, let’s discuss the physical properties of these alkanes.

Let’s start with the physical states of these alkanes.

Lighter alkanes such as methane, ethane, propane and butane exist in gaseous form.

While the alkanes containing from five carbons to seventeen carbon atoms exist in liquid forms.

When we consider more heavier alkanes, these compounds exist in waxy solid forms.

Now, we will discuss about the solubility of alkanes.

When we try to dissolve alkanes in water, these are insoluble.

But alkanes are soluble in benzene, ether, and other organic solvents.

This happens due to the non-polar nature of alkanes. So it will be soluble in non-polar solvents and will be insoluble in polar solvents

This also makes the liquid alkanes a good solvent for other non-polar substances.

Let’s see the colour and odour of alkanes.

These alkanes are colourless and odourless in nature.

Now, we will discuss the trends in the boiling and melting points of alkanes.

If we talk about the boiling points of alkanes, it gradually increases as the number of carbons in the chain increases.

Similarly, the melting points also increase with the increase in number of carbons in the chain.

Here, we can see that as we move from methane to propane, melting point decreases. This is an exception

The increase in the boiling, as well as the melting point, is due to the larger molecular size of the alkanes in longer chain

Boiling and melting points are affected by branching in chains also

The straight chain alkanes have higher boiling point than its branched chain isomers.

This is because the boiling point of a substance is higher when attraction between molecules is high

The straight chained isomers have a larger surface area. This means the interaction between their molecules are higher than the branched isomers

The trends of melting point are little complicated. This is because melting point depends on how well molecules are packed

When we consider a linear and a branched molecule, the linear molecule is better packed than branched molecule

So the linear isomer has higher melting point than the branched molecule

But when we consider a branched molecule and a highly branched molecule, the story changes. Highly branched molecules have a spherical shape which can be packed better than other shapes

So the highly branched isomer has higher melting point than the branched molecule

Let’s discuss some of the important uses of alkanes.

Alkanes are the hydrocarbons which produce enormous amount of energy on burning.

This is why these are used as fuels in LPG, CNG, etc.

Alkanes are also used in the formation of various alcohols, aldehydes and organic acids.

Revision

Alkanes are found in various forms based upon the number of carbons in the chain.

These alkanes are colourless and odourless in nature.

The boiling points in alkanes increases as the number of carbon increases in the chain.

The melting points in alkanes also increase as the number of carbon increases in the chain except for methane, ethane and propane.

Alkanes are used as fuels e.g. petrol, LPG, CNG, etc.

The End