Question

Which of the following best explains how hydrogen bonding affects the heat of vaporization for water?

Answer 1

When molecules are heated, they get excited. They move around faster as they gain more energy. H2O is a polar molecule (has a plus end and a minus end). This is because the O takes the e- from the H atoms in order to gain a stable octet in a process called hydrogen bonding. Now we have a H2O where the two H atoms are positively charged and the O is negatively charged. Positive attracts to negative and water molecules stick together. They make intermolecular dipole-dipole bonds and these bonds are very strong. Because the molecules are being held tightly in place by these bonds, the H2O molecules don't move much when heated. It takes more and more heat to move the molecules, causing water to have a high specific heat capacity.

Read more: http://wiki.answers.com/Q/Why_does_water_have_a_high_and_specific_heat_capacity#ixzz1jDGKSUf0

Answer 2

Copied and pasted from my answer to this very same question last night:

I think it's b.

Think about the physical basis of hydrogen bonding. Oxygen is very electronegtive - it's 'pull' on bonding electrons is stronger than hydrogen. That means that oxygen attracts the two bonding electrons more closely and has a partial negative charge; the two hydrogens get a partial positive charge. In solution, these partial charges attract one another. This creates a hydrogen bond, a very strong force between different molecules. To overcome this force - that is, to vaporize the solution - you need to put in a lot of energy. So D is obviously out of the question: you need more, not less energy to disrupt the bonds.

And B is the answer.

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