Question

Why do alkenes have lower boiling points than alkanes?

Answer 1

Alkenes contains a carbon-carbon double bond. This carbon-carbon double bond changes the physicals properties of alkenes. At room temperatue, alkenes exist in all three phases, solid, liquids, and gases. Melting and boiling points of alkenes are similar to that of alkanes, however, isomers of cis alkenes have lower melting points than that of trans isomers. Alkenes display a weak dipole-dipole interactions due to the electron-attracting sp2carbon.

Alkenes are a family of hydrocarbons (compounds containing carbon and hydrogen only) containing a carbon-carbon double bond. The first two are:

ethene ( C2H4 )propene (C3H6)

You can work out the formula of any of them using: CnH2n. The list is limited to the first two, because after that there are isomers which affect the names.
Hope it helps!!!!

Answer 2

Inter molecular forces of alkene gets strong with increase the size of molecule so it's boiling point is low.....