Question

15. Explain why the heat of vaporization of a substance is much greater than the heat of fusion for the same substance.

Please show all work with the correct answer. Thank you!!!!

Answer 1

15)

latent heat of fusion : it is the heat required to change a substance from a solid (ice) to a liquid (water) or liquid to solid with out change in temperature .

latent heat of vaporization : it is the heat required to change a substance from a liquid (water) to a gas (steam) or gas to liquid.

The latent heat of fusion and vaporization both involve the heat required to change the state of a substance without a change in temperature.

In solids, the molecules are very close together and the attraction between the molecules are great. This causes a substance to have a structure in which the molecules have little freedom to move, as we would see in the case of ice.

In the case of a liquid, the molecules are closely spaced, though not as closely spaced as a solid, they have more freedom to move and the intermolecular forces are weaker that that of a solid.

Now we heat a solid turning it into a liquid, we increase the kinetic energy of its molecules, moving them further apart until the forces of attraction are reduced to allow it to flow freely. Keep in mind the forces of attraction still exists.Now as we heat a liquid, turning it into a gas, the kinetic energy of the molecules are increased to a point where there are no forces of attraction between the molecules.

The energy required to completely separate the molecules, moving from liquid to gas, is much greater that if you were just to reduce their separation, solid to liquid. Hence the reason why the latent heat of vaporization is greater that the latent heat of fusion