Ch 14 Test Review Answers 1-5 2005-6

1. What is meant by the latent heat of fusion.

            the amount of heat required to melt 1 gram of a substance

2. What is meant by the latent heat of vaporization.

            the amount of heat required to vaporize or change 1 gram of a liquid to a gas

3. Are changes in state physical or chemical changes? Explain.

Physical changes: No chemical bonds are broken during the change and no new substances result (no changes in the intramolecular forces take place).

4. Which is larger, the latent heat of vaporization of water or its latent heat of fusion? Explain.

The molar heat of vaporization is larger because in order to form a vapor, the molecules have to be moved much farther apart, all the intermolecular forces must be overcome.

5. Why does the boiling point of a liquid vary with altitude?

Because the atmospheric pressure (against which the vapor must be expanded during boiling) decreases with altitude.

6. Order the intermolecular and intramolecular forces according to strength (strongest first).

Network solid, Ionic, metallic, covalent, hydrogen bonding, dipole-dipole, London Dispersion  Forces

7. Sketch the H-bonding of NH₃, What other molecules tend to form H-bonds?

         Any molecule in which H is bonded to Fluroine, Oxygen, or nitrogen.

8. What causes London Forces?

London Forces are instantaneous dipole forces. At any given instant, there may be more electronic charge on one side of the nucleus than the other, which results in a separation of charge and a small dipole moment.