[meenu]

Each of the following substances is a gas at 25°C and 1 atmosphere pressure. Which one will liquefy most easily when compressed at a constant temperature?  
F2 ;  H2  ; HF  ; SiH4   ; or Ar
please explain with reason

[Guitarmaniac86]

Each of the following substances is a gas at 25°C and 1 atmosphere pressure. Which one will liquefy most easily when compressed at a constant temperature?  
F2 ;  H2  ; HF  ; SiH4   ; or Ar
please explain with reason

Gaseous molecules are assumed to have very little, or next to no attraction between each molecule due to the relatively large distance between each molecule. When a gas is compressed, the relative distance between each molecule is reduced and hence intermolecular attractions become important.

The more polarised a molecule is, the more likely it is to liquefy as the gas is compressed. Look at the molecules you have and look at which is the most polarised. Looking at the electronegativity of each atom in each molecule may help you to work this out. The larger the difference in values of electronegativity between each atom in the molecule, the more polarised it is. Therefore, you can work out which one is easily compressed.

Hope that helps.

(Read up on the Joule-Thompson Effect, it should explain it better than I have.)

[cliverlong]

Some intersting stuff on the practical  processes of compression, evaporation and cooling to liquefy gases here

http://www.linde.de/international/web/linde/like35lindecom.nsf/docbyalias/page_ch_chronicle_18911934details_1

but not directly related to your theoretical question on the boiling points of various gases.

Clive

[Astrokel]

hey meenu,

Hope this helps!

http://www.chemicalforums.com/index.php?topic=26296.msg98909#msg98909