Physical and Chemical Properties of Alkanes

Physical properties of a compound are those characteristics that can be observed and measured without causing any change in the chemical composition or identity of the substance. These properties relate to the substance's physical state, appearance, and behavior under various conditions. They provide valuable information about how a substance interacts with its surroundings and other substances without undergoing a chemical reaction.

Physical properties of alkanes include the following:

• Physical state Lower molecular weight alkanes are gases.
• Methane, ethane, propane and butane are gases at ordinary room temperature.
• Higher alkanes up to those having 17 carbon atoms are liquids; higher alkanes are solids at room temperature.
• Melting and boiling points Homologous alkanes show increase in melting and boiling points.
• Similar to the behavior of elements in the same group in a periodic table.
• Like all other organic chemicals are insoluble in water. They are however soluble in organic liquids.
• Alkanes are non-polar and are hence soluble in other non-polar liquids and not in water, as water is a polar molecule.

They will react with strong oxidising chemicals like chlorine when heated or subjected to u.v light.
A substitution reaction occurs and a chloro-alkane is formed e.g a hydrogen atom is swapped for a chlorine atom and the hydrogen combines with a chlorine atom forming hydrogen chloride.
This process is called halogenation.
A halogen atom attacks the alkane, substituting itself for a hydrogen atom.
This substitution may occur many times in an alkane before the reaction is finished.

Alkanes, along with all other types of hydrocarbon, will burn in an excess of oxygen to give carbon dioxide and water only as the products

CH₄ (g) + 2O₂(g) → CO₂(g) + 2H₂O(g)

The general reaction is as follows

C_nH_2n+n (g) + (1.5n+0.5)O₂(g) → nCO₂(g) + (n+1)H₂O(g)

If there is not enough oxygen present then instead of carbon dioxide, carbon monoxide, CO, is produced.
Carbon monoxide is particularly toxic and absorbed into blood, through respiration, very easily.

Alkanes are saturated hydrocarbons
Molecules of saturated hydrocarbons contain only single bonds between all carbon atoms in the series
Hence their reactivity with other chemicals is relatively low