Properties and reactions of Alkanes

Alkanes are saturated hydrocarbons. This means they contain only carbon and hydrogen with no double bonds. The physical properties of alkanes depend on the number of carbons in the molecule Alkanes with 4 carbons or less are gases at room temperature Alkanes with 5-15 carbons are liquid at room temp Alkanes with 16 or more carbons are solid at room temp

Alkanes are non-polar and are not soluble in water. They will dissolve in other non-polar substances and can be useful as solvent for non-polar substances. Alkanes have a density of less than 1g.cm -3 and will float in water. Alkanes are flammable. Gaseous alkanes will react with oxygen to give off heat.

Combustion Combustion is the reaction of hydrocarbons with oxygen. Complete combustion produces carbon dioxide and water C n H 2n+2 + O 2  CO 2 + H 2 0 Incomplete combustion produces carbon or carbon monoxide C n H 2n+2 + O 2  CO + H 2 0 Combustion is often a combination of complete and incomplete reactions C n H 2n+2 + O 2  CO 2 + CO + C + H 2 0

Balancing combustion reactions 1.Identify combustion product – CO 2 or CO 2.Balance C atoms with CO 2 or CO 3.Balance H atoms with H Balance O atoms with O 2

Production of Alkanes Alkanes are found in nature in crude oil or natural gas. Long chain alkanes are broken up in a process called cracking into alkanes and alkenes. Commercial cracking supplies excess H 2 to the reaction to produce all alkanes

Alkane reactions Alkanes can undergo substitution reactions where the hydrogens are substituted (replaced) for another atoms CH 4 + Cl 2  CH 3 Cl Methane and Chlorine will react together in the presence of UV light to produce haloalkanes. The substitution will repeat until CCl 4 is produced UV light

Primary, Secondary and Tertiary haloalkanes Haloalkanes and alcohols can be classified as primary, secondary or tertiary. This denotes how many carbons are attached to the carbon that the halogen (or hydroxyl group) is attached to. If there is only one carbon attached it is primary If there are two carbons it is secondary If there are three carbons it is tertiary