Re: Why is there an increase in boiling point from H sulphide to H selenide?

Dear Michelle,

You were right about the ionisation energy having an effect, but the change in 
boiling piont is due to the Entropies of the hydrides.  H2S has an entropy of 
-33.6 while H2Se has a value of +15.9.  This means that H2Se has more order in 
its system, so needs more energy to make it disordered (boil) and therefore has 
a higher boiling point than H2S.

I hope this has cleared up your query. Good luck in the exam.

Thanks for asking.

Yours Sincerly Peter D. Traill