Question

A. During the vaporization process, how does the energy of the molecules of the substance change as a result of the heat it absorbs?

b. How does the heat of vaporization of water compare to the heats of vaporization of other, similar substances? How does this difference relate to intermolecular forces?

c. How much heat is needed to melt 3.0 kg of ice at its melting point? The latent heat of fusion for water is 333 kJ/kg. Show your work.

d. When the temperature is expected to drop below freezing, a citrus farmer sprays water on the trees and fruit. Write two or three sentences to explain why the farmer uses this technique to protect the trees and fruit from freezing. Hint: Remember that liquid water has more potential energy than ice.

Answer 1

a) Molecules' energy increases cause they consume heat, increase their speed and thus the temperature of the substance increases.

b) For acetone heat of vaporization is 539390 J/kg, for water - 2257000, for aluminum - 1050000 J/kg. We see that hard and dense substances require much more energy to destroy molecular bindings.

c) Q=L*m=333000*3=999000 J.

d) Because while becoming ice water looses energy - this energy represents heat that can warm up the fruits.