Understanding Properties of Alkanes

Alkanes are saturated hydrocarbons made up of hydrogen and carbon atoms joined by sigma bonds. As a result, alkanes may be synthesized utilizing a variety of processes and starting materials. Alkanes are the primary ingredients of crude oil and the building blocks of the vast majority of petroleum products. Alkanes are also known as saturated and saturated hydrocarbons. Carbon atoms are bound together to form a chain (linear or branching alkanes), a circle (cyclic alkenes), or a combination of both. Alkanes are distinguished from other hydrocarbons by the fact that they are entirely hydrogen-saturated. This means that adding extra hydrogen atoms to these compounds will weaken the carbon backbone.

Physical Properties of Alkane

Alkanes may be found in all three states: gas, liquid, and solid. At room temperature, ethane, butane, methane and propane are all gases. Pentane, hexane, and heptane are liquids with unbranched structures. Solids are alkanes having a greater molecular weight.

• Solubility

Alkanes are a kind of chemical compound that is non-polar. Because water is a polar solvent, alkanes do not dissolve in it. They are hydrophobic chemicals. They dissolve in organic solvents that are non-polar or mildly polar. Alkanes are employed as metal lubricants and preservatives because they protect the metal surface from contact with water, hence preventing corrosion.

• Density

Alkane densities are lower than the density of water. Their density is roughly 0.7 g mL-1, as compared to the density of water, which is 1.0 g mL-1. When we mix an Alkane with water, for example, the Alkane layer separates on top of the water because Alkanes are less thick than water and are insoluble in water.

• Boiling points

The boiling point of unbranched alkanes gradually increases as the number of carbon atoms and molecular weight increase. Larger molecules have a larger surface area, which allows them to create more van der Waals interactions (London force interactions). Despite the fact that they are modest intermolecular interactions, they elevate boiling temperatures and hence prevent vaporisation. In general, branched alkanes with the same number of Carbon atoms have lower boiling points than unbranched alkanes with the same number of carbon atoms. Differences in boiling temperatures occur because branched alkanes are more compact with a limited surface area, allowing for less surface area for London force interactions. The boiling temperatures of branched alkanes are lowered as a result.

• Melting points:

This follows the same pattern as melting points for n-alkanes; melting point increases with molecular weight. However, the melting temperatures of alkanes with an even number of carbon atoms and those with an odd number of carbon atoms varies somewhat. Because they are tightly packed into a solid form, alkanes with an even number of carbon atoms have higher melting temperatures. As a result, melting them requires a higher temperature throughout the alkane series. As a result, the melting point fluctuation does not follow a smooth curve along the alkane series. The melting points of branched alkanes are greater than those of n-alkanes with the same number of carbon atoms. A branching structure results in a more compact 3D structure. It quickly forms a solid structure and has a high melting point.

Chemical Properties of Alkane

Most reagents have little effect on alkanes. Under suitable circumstances, however, alkanes undergo the following type of reaction. 

• Combustion

A combustion reaction is a chemical process that occurs between material and oxygen, resulting in the release of heat and light (usually as a flame). When burned in the presence of enough oxygen, alkanes burn and create carbon dioxide and water.

• Halogenation

A halogenation reaction is a chemical reaction between an alkane and a halogen in which the halogens replace one or more hydrogen atoms.

Both chlorination and bromination are common halogenation reactions. Iodination is too slow and fluorination is too fast. In the presence of light or when heated, methane interacts with chlorine.

• Aromatisation

 At high temperatures and in the presence of a catalyst, alkanes with six to ten carbon atoms are transformed into homologous benzene. Aromatization is the name given to this process. It is caused by the simultaneous cyclisation and dehydrogenation of alkanes.

• Pyrolysis

Pyrolysis is described as the thermal degradation of organic compounds into smaller pieces in the absence of air using heat. ‘Pyro’ is Greek for ‘fire,’ and ‘lysis’ is Greek for separating.’ Alkane pyrolysis, also known as cracking. When alkane vapours are pushed over red-hot metal in the absence of air, they decompose into simpler hydrocarbons.

Uses of Alkane

• The exothermic character of the alkane combustion process is the reason it is widely used as fuel. Natural gas contains methane, which is utilized in home heating. 
• LPG gas is a mixture of propane and butane that is used for residential cooking. 
• GASOLINE is a complicated combination of several hydrocarbons that is utilized as a fuel in internal combustion engines.
• Carbon black is used to make ink, printer ink, and black pigments. It’s also used to make fillers.

Conclusion: 

Alkanes are hydrocarbons that have the formula CnH2n+2. All of the carbon atoms are SP3 hybridized, forming sigma bonds that point to the corners of a tetrahedron. Both the boiling and melting points rise as the molecular weight rises. The branching of the chain has a significant influence on both the melting and boiling points, although in opposing directions. The boiling point of an alkane is reduced when it is branched; conversely, the melting point of an alkane is increased when it is branched. The fluctuation in boiling point and melting point for an n-alkane series displays an upward trending pattern. Nonetheless, the melting point graph does not have a smooth form. Alkanes are chemically stable and seldom participate in chemical reactions. They are soluble in non-polar or weakly polar organic solvents but insoluble in polar solvents. Alkanes have a lower density than water. Alkanes exhibit isomerism, which means that one chemical formula can have many molecular configurations. Their physical and chemical characteristics vary depending on the structure.