freezing

from liquid to solid

You dont have to be an ice climber to enjoy ice. Skating and fishing are two other sports that are also done on ice. What is ice? Its simply water in the solid state. The process in which water or any other liquid changes to a solid is called freezing. Freezing occurs when a liquid cools to a point at which its particles no longer have enough energy to overcome the force of attraction between them. Instead, the particles remain in fixed positions, crowded closely together, as shown in the Figure 1.1.

freezing point

The temperature at which a substance freezes is known as its freezing point. Freezing point is a physical property of matter. The freezing point of pure water is 0 C. Below this temperature, water exists as ice. Above this temperature, it exists as liquid water or water vapor. Many other substances have much lower or higher freezing points than water. You can see some examples in the Table 1.1. The freezing point of pure water is included in the table for comparison. Substance Helium Oxygen Nitrogen Pure Water Lead Iron Carbon Freezing Point ( C) -272 -222 -210 0 328 1535 3500 Q: What trend do you see in this table? A: Substances in the table with freezing points lower than water are gases. Substances in the table with freezing points higher than water are solids. Q: Sodium is a solid at room temperature. Given this information, what can you infer about its freezing point? A: You can infer that the freezing point of sodium must be higher than room temperature, which is about 20 C. The freezing point of sodium is actually 98 C.

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questions

which of these substances has the highest freezing point?

-->  a) lead

b) helium

c) oxygen

d) nitrogen

which of these substances has a lower freezing point than pure water?

-->  a) salt water

b) carbon

c) sodium

d) iron

a liquid freezes because its particles lose energy.

-->  a. true

b. false

freezing point is a chemical property of matter.

a. true

-->  b. false

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