If I have a list of organic compounds....how can I determine which one has a higer melting point or boiling pt

Answer 1

Arrange them in order of Mr. Then look at the intermolecular forces.
The ones which can hydrogen bond will be highest, then the ones which are polar, and then the ones which are non-polar.

For the non-polar ones, look at the shape of the molecule - long thin ones have higher MP and BP than short, fat ones.

Answer 2

Melting point is the point where particles in a substance have enough thermal energy (combination of kinetic and potential) so they can now slip past each other instead of staying in the crystal structure of the solid. The heat that the material must gain for the material to do this is called it's heat of fusion. Boiling point is the temperature at which a substance begins to vaporize but pressure is also a consideration. For example, water will begin boiling at 100 degrees Celsius if it is at sea level. But since it is pressure dependent then it will boil at a lower temperature if the pressure outside the substance is lower (like up on a mountain). A substance will boil if enough energy is added to it, and this energy increases the pressure within the substance. When the pressure within a substance is greater than the pressure outside a substance, the substance will boil and it's boiling point has been reached. Boiling point is dependent on Pressure AND Temperature. The heat needed to boil (or vaporize) an amount of stubstance is called it's heat of vaporazation.

Answer 3

In reality, what most scientists would do is look the information up! We don't have time to do melting point or boiling point experiments in the lab, when the information is already out there somewhere.

I use a big book called the CRC which has properties of all the chemicals. Otherwise, try going to wikipedia.org and searching for the compound by name.

For instance phthalic anhydride
http://en.wikipedia.org/wiki/Phthalic_anhydride
melting point = 131 C, boiling point = 284 C

Answer 4

the bigger the molecule the bigger the forces that have to be overcome to melt or boil. the stronger the bonds, the higher the bp and mp.

Answer 5

there are many points to check the boiling and melting points....
1= the size of anion and cation
2=any special forces present
3= hydrogen bonding if present.... inter or intra
4=lattice energy.............
and also the molecular weight

Answer 6

The smaller molecular weight has the lower mp and bp