Physical properties of alkanes

Alkanes are organic compounds consisting entirely of single-bonded carbon and hydrogen atoms and have no additional functional groups. Alkanes are divided into three groups: linear straight-chain alkanes, branched alkanes, and cycloalkanes. They have the general formula CnH2n+2. Alkanes are saturated hydrocarbons as well. Alkanes are the most basic and least reactive hydrocarbons, consisting completely of carbon and hydrogen.. They are particularly significant commercially since they are the main component of gasoline and lubricating oils, and they are widely used in organic chemistry, however pure alkanes are usually used as solvents. The lack of unsaturation distinguishes an alkane from other molecules that also contain only carbon and hydrogen.

That is, it lacks the highly reactive double and triple bonds found in organic chemistry. Their lack of reactivity under normal laboratory circumstances makes them a very dull, yet extremely significant, component of organic chemistry. The energy enclosed within the carbon-carbon bond and the carbon-hydrogen link is rather considerable, as you will learn later, and their rapid oxidation produces a lot of heat, which is often in the form of fire.

Alkanes have Physical and chemical properties

Alkane Physical Properties:

• Alkanes have no color
• Alkanes are lighter than water and have a lower density
• Alkanes dissolve more readily in non-polar than polar solvents because they are nonpolar molecules
• Alkanes do not dissolve in water
• The melting and boiling temperatures of shorter chain alkanes are low, but as the number of carbon atoms in the carbon chain rises, the melting and boiling values of alkanes rise

Alkane Chemical Properties:

• Alkanes have low reactivity

• Strong acids, bases, oxidizing agents and reducing agents do not react with alkanes
• Alkanes are valuable as fuels because they burn and release energy
• In the presence of ultraviolet light, alkanes will react with halogens such as chlorine gas and bromine water

Description of Physical properties of alkanes

Following are the physical properties of alkanes:-

Boiling point

The boiling points displayed are for “straight-chain” isomers, of which there are several. The first four alkanes are gasses at ambient temperature, and solids don’t appear until roughly C17H36; however, this is only an estimate because different isomers have varying melting and boiling points. There is no substantial bond polarity because there is no major difference in electronegativity between carbon and hydrogen. The only attraction between one molecule and its neighbors will be Van der Waals dispersion forces in the case of a fully symmetrical molecule like methane. These forces will be quite little for a molecule like methane, but they will develop as the molecules become larger. Alkanes’ boiling temperatures grow in proportion to their molecular size as a result. The more branched the chain is when you have isomers, the lower the boiling point tends to be. Shorter molecules have less Van der Waals dispersion forces, which only function at very short distances between molecules. Short, fat molecules have a harder time lying as close together as long, thin molecules.

Solubility

Alkanes (both alkanes and cycloalkanes) are water-insoluble but soluble in organic solvents. Liquid alkanes, on the other hand, are effective solvents for a wide range of non-ionic organic molecules.

Solubility in water

The following must happen when a molecular compound dissolves in water:

• Within the material, disrupt the intermolecular forces
• These are the Van der Waals dispersion forces in the case of alkanes
• In order for the substance to fit between the water molecules, the intermolecular forces in the water must be broken
•  Hydrogen bonds are the fundamental intermolecular attraction in water

Breaking either of these attractions requires energy, albeit the amount of energy required to break the Van der Waals dispersion forces in methane is small compared to the hydrogen bonds in water. To simplify things, a material will dissolve if enough energy is released when new bonds between the substance and the water are formed to compensate for the energy expended in breaking the original attractions. Van der Waals forces are the sole new attractions between the alkane and water molecules. The alkane does not dissolve because these forces do not release enough energy to compensate for the energy required to break the hydrogen bonds in water.

Organic solvent solubility

When an alkane dissolves in an organic solvent, the Van der Waals forces are broken and new Van der Waals forces are formed. There is no barrier to solubility because the two processes almost cancel each other out energetically.

 Color of alkanes

• Colorless gasses range from methane to butane
• Colorless liquids made up of alkanes with 5 to 19 carbons
• Colorless waxy solids with more than 20 carbon atoms are known as alkanes

Alkanes’ Density

• The density of alkanes is lower than that of water (alkanes will float on top of water)
• With increasing molar mass, density rises

Conclusion

Alkanes are compounds made completely of carbon and hydrogen atoms joined together by single carbon-carbon and carbon-hydrogen bonds.

Alkanes are colorless and odorless by nature. The intermolecular Vander Waal force attracts alkane molecules. Alkanes with stronger intermolecular van der Waals forces have higher boiling points. For the same reason as the boiling point, the melting point of alkanes follows a similar pattern. That is, the melting point rises with the size of the molecule.

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