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1) How do hydrogen bonds contributes to the high melting and boiling points of water?

1) How do hydrogen bonds contributes to the high melting and boiling points of water?
 
2) What functional groups of biomolecules can form hydrogen bonds?
 
3) Describe what happens when a crystalline salt such as NaCl dissolves in water in terms of the enthalpy and entropy of the system. 
 
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1 Answer

1.  Hydrogen bonds are relatively strong intermolecular forces, and thus it takes a lot of energy to break these bonds.  This is why the boiling point of water is high, because a lot of heat (energy) is needed to break the intermolecular bonds holding the water molecules together.
 
2.  Any groups where the H is bonded to O, N or F.  So, some examples would be carboxyl groups (COOH), amines (NH2), phenols (benzene with an OH), etc.
 
3.  Water molecules get between the Na+ and Cl- of the NaCl.  The entropy increases because the solution is much less ordered than the crystalline solid.  Enthalpy also increases during the dissolution process, and energy is needed to break apart the Na and Cl ions.