Given the molecules H2S and H2O are both in the same chemical Group, which do you predict to have the higher boiling point and why? Be specific, points will be awarded on the appropriate use of terminology and concepts.

Answer 1

GENERALLY, the boiling point of a compound increases with the molar mass; therefore, one would expect H2S to have a higher boiling point than H2O. However, hydrogen bonding is possible in H2O which causes the boiling point of H2O to be MUCH higher than expected, and it is. Hydrogen bonding does not exist in H2S since the electronegativity of S is not as high as oxygen in H2O. If you look at the trend in boiling points from H2Te, H2Se, H2S, H2O one would expect the boiling points to get successively lower as one goes up the chart. Google to see the diagram. I can't draw it on this site but you can find it on google. It's dramatic.