Year 12s: what will be the first way you research your future options? >>

Question help

Why is the answer to this question A? I assume it has something to do with hydrogen bonding A4D5F1CE-6E5A-4038-A2A8-5B20262F2018.jpg.jpeg

Reply 1

username3249896

The boiling points increase from NH3 to BiH3 since van der Waal forces get stronger.

However NH3 has hydrogen bonds which are much stronger than van der Waal forces. Hence it has a higher boiling point than PH3 hence A

Reply 2

Masterchief1345

Original post by BobbJo

Ok thanks. So would it be instantaneous dipole-induced dipole forces that form between the molecules from PH3 to BiH3?

Reply 3

username3249896

Original post by Masterchief1345

Ok thanks. So would it be instantaneous dipole-induced dipole forces that form between the molecules from PH3 to BiH3?

All from NH3 to BiH3 have id-id forces. NH3 has hydrogen bonds in addition to this. Since H-bonds are much stronger, NH3 has a much higher bp than PH3 and AsH3.

Since id-id forces get stronger down the group, you can see that eventually the H-bonds are eventually overshadowed by the id-id forces in SbH3 and BiH3.

So the trend should be an increase. This trend is only broken by ammonia due to the H-bonds