# Why does hydrazine have a higher boiling point than water?

$$\ce{N2H4}$$ has a boiling point of 114 °C, which is higher than the boiling point of water. Why is this so?

Both $$\ce{N2H4}$$ and $$\ce{H2O}$$ have two lone pairs, so the number of hydrogen bonds per molecule seems to be the same. Also, the $$\ce{O...H}$$ hydrogen bond (21 kJ/mol) is stronger than the $$\ce{N...H}$$ hydrogen bond (13 kJ/mol). So, given this information, why is it that $$\ce{N2H4}$$ has a higher boiling point?

• Maybe partially due to the molecular weight difference? – Ed V Mar 3 '20 at 21:04
• H2O isn't fully using it's lone pairs, some O atoms are getting only one, not two H-bonds – Mithoron Mar 3 '20 at 21:16
• The reason is in the molar masses. For N2H4 it is 32 g/mol. For H2O, it is 18 g/mol. Heavier moles must get more energy for passing in the vapor phase. – Maurice Mar 3 '20 at 21:19
• Being a larger molecule, i suspect you can excite more vibrational modes before the hydrogen bonds break. – Karl Mar 3 '20 at 23:04