Concept explainers
Lakes freeze from top down we all know that ice cubes float in a glass of water. Why? Virtually every substance contracts when it solidifies—the solid is denser than the liquid. If this happened to water. Ice cubes would sink to the bottom of a glass, and ice sheets would sink to the bottom of a lake. Fortunately, this doesn't happen. Liquid water expands by
But this is not the only special thing about water. While the density of most substances increases when they are cooled, water density shows a very peculiar temperature dependence (see Figure 13.17). As the temperature decreases, water density increases, but only until
Note that if water were most dense at the freezing point, then in the winter the very cold water at the surface of lakes would sink in this case the lake would freeze from the bottom up, and an life in it would be destroyed.
The expansion of water when it freezes has another important environmental benefit: the so-called freeze-thaw effect on sea memory rocks. Water is absorbed into cracks in these rocks and men freezes in cold weather. The solid ice expands and cracks the rock, like a wood-cutter splitting logs. This continual process of liquid w after absorption, freezing and cracking releases mineral and nitrogen deposits into the soil and can eventually break the rock down into soil.
Why does water freeze from the top down?
a. The denser water at
b. The less dense ice at
c. The denser water at
d. Because of both a and b
e. Because of both b and c
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