Alkanes have no double or triple bonds, alkenes have one or more double bonds and alkynes have one or more triple bonds. Alkanes, alkenes and alkynes are all types of hydrocarbons.
With no multiple bonds, alkanes are essentially chemically inert, but they are highly flammable when exposed to high-temperature energy sources. The combustibility of alkanes, such as butane, makes them useful in lamps, cook stoves and lighters.
The double and triple bonds in alkenes and alkynes make those molecules much more reactive. Alkenes react quickly to halogens, adding two halogen atoms or one halogen atom and a hydrogen atom across multiple bonds. Because alkenes and alkynes react so readily with halogen molecules, these reactions can be used to test for the presence of these unsaturated molecules in hydrocarbon mixtures.