Question

Compare the boiling points of 1-pentyne and 1-octyne. Compare the vapor pressure curves of 1-butene and 1-heptene.

Answer 1

1-pentyne  boiling point is 40 degrees C it is lower than the one for 1-octyne which is 126 degrees C the vapor pressure for 1-butene is higher at low temperatures than 1-heptene.These are due to the difference in the length of the chains.  The strong molecular forces are stronger in large molecules.  There is more energy needed to move large molecules to the vapor phase when in liquid form.

Answer 2

Did your answers include all of the following?

1-pentyne has a lower boiling point than 1-octyne.  

1-butene has higher vapor pressures at lower temperatures than 1-heptene.

The differences in boiling points and vapor pressures result from differences in the chain lengths of the molecules.

Larger molecules have stronger intermolecular forces of attraction than smaller molecules.

More energy is required to move larger molecules into the vapor phase from the liquid state.