The Student Room Group

Quick Hydrogen Bonding Question

I understand how the relatively strong hydrogen bonds between water molecules result in water having a relatively high melting point. However if when water (s) melts and these hydrogen bonds collapse, how is water still able to have such a relatively high boiling point as said in the textbook (since surely there would be no hydrogen bonds between the water molecules in its liquid state)?
Original post by Ecconomist
I understand how the relatively strong hydrogen bonds between water molecules result in water having a relatively high melting point. However if when water (s) melts and these hydrogen bonds collapse, how is water still able to have such a relatively high boiling point as said in the textbook (since surely there would be no hydrogen bonds between the water molecules in its liquid state)?


There are still hydrogen bonds in the liquid state ...
Reply 2
Original post by charco
There are still hydrogen bonds in the liquid state ...


Oh okay that'd make sense; it's just the textbook says that 'when ice melts, the rigid hydrogen bonds collapse, allowing the H"2"O molecules to move closer together' which suggested to me that the only intermollecular from then on were vdw / pd forces.

Thank you.
Original post by Ecconomist
Oh okay that'd make sense; it's just the textbook says that 'when ice melts, the rigid hydrogen bonds collapse, allowing the H"2"O molecules to move closer together' which suggested to me that the only intermollecular from then on were vdw / pd forces.

Thank you.

Liquid water has vdw/pd and H-bonds.
In ice the molecules are held in an open 3d lattice with 2 H bonds per molecule. In liquid water the rigidity is lost and the molecules are not held in place but the main interaction is still H bonds. The molecules will be closer together in liquid water because the molecules are not being held in a rigid 3d structure. Water has its greatest density at 4 degrees Celsius.

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