Instructor: Dr. Bruce Law, CW
327, Tel: 532-1618.
REVIEW QUESTIONS OF Home Work 12
R17.28. A liquid absorbs thermal energy when it turns into a gas. This absorbed thermal energy causes the molecules to move more rapidly thus break the bonds between the liquid molecules as the liquid changes into a gas. When the liquid turns into a solid, thermal energy is given off. As less thermal energy is available to the molecules, they vibrate less and hence solidify into a solid.
R17.29. A gas gives off thermal energy as it turns into a liquid. A solid absorbs thermal energy as it turns into a liquid.
R17.32. The latent heat of vaporization for water is large. Therefore if you finger is wet a lot of the heat energy from the hot clothes iron goes into vaporizing the water on your finger. (If your finger was dry then you would be more likely to burn your finger in touching the hot iron.)
E17.46. Water possesses a large specific heat capacity and a large latent heat of freezing, therefore, a lot of heat energy must be removed from the water in order to freeze it. As the temperature of the surrounding air drops below 0C, heat flows from the warmer water on the fruit trees into the colder air. This warms the air and moderates the air temperature around the fruit trees. The fruit will not be damaged (by dropping to very low temperatures below 0C) provide the water on the fruit trees does not freeze.