Question

For each of the following pairs of molecular substances, predict which member of the pair would have the higher boiling point.

Br2
Cl2

NH3
PH3

SO2
O3

H2S
SiH4

Answer 1

It would be great if you could explain your reasoning, too. I'm pretty confused on how to do this.

Answer 2

BP's are influenced by the intermolecular forces that a molecule can exhibit with adjacent molecules. Do you know these and their relative strengths?

Answer 3

Sort of. I know London dispersion forces are the weakest IMFs, induced dipoles are very weak, and that hydrogen bonding is the strongest one..

Answer 4

sort of, it goes: london<dipole-induced dipole<dipole-dipole<ion-dipole<ionic

the substances you're dealing with are simple, and only include:

london<dipole-dipole<ionic

H-bonds are dipole-dipole, because of the high magnitude of the dipole, they're the strongest dipole-dipole.

So, now all you have to do if figure out which molecules have which IMFs.

Answer 5

oh and for london dispersion forces higher molecular weight (i.e. size) higher force (because there are more electrons to be polarized).

Answer 6

The first one with bromine and chlorine...since chlorine has a bigger molecular size, it would have a higher boiling point, right?

As for the second one...since hydrogen is bonded to nitrogen, it has hydrogen bonding, and hydrogen bonds especially close to nitrogen, oxygen, and fluorine, so NH3 would have the higher boiling out...

For the third one...O3 is nonpolar, while SO2 is polar, so SO2 requires more energy to break apart...right?

And the last one...not sure, actually.

Answer 7

Bromine is actually bigger than Chlorine.

NH3 is correct.

SO2 is correct

H2S same geometry as water (sulfur also has 6 valence electrons)
SiH4 same geometry as methane, CH4 (non-polar)

Answer 8

Oh, oops, my mistake. So then H2S is the one with the higher boiling point, since there are only 2 bonds.

Answer 9

I think?

Answer 10

hm it does have a higher BP because its polar.

Answer 11

Got it. Thanks so much! :D

Answer 12

no problem !