CK-12 Physical Science Concepts - For Middle School

2.18. Freezing http://www.ck12.org

FIGURE 2.38

water. You can see some examples in theTable2.3. The freezing point of pure water is included in the table for
comparison.

TABLE2.3:Freezing Points

Substance Freezing Point (°C)

Helium -272

Oxygen -222

Nitrogen -210

Pure Water 0

Lead 328

Iron 1535

Carbon 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.

Summary

• Freezing is the process in which a liquid changes to a solid. It 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.


• The freezing point of a substance is the temperature at which it freezes. The freezing point of pure water is
  0°C.

Vocabulary

• freezing: Process in which a liquid changes to a solid.

Explore More

Road crews put salt on icy roads, and salt is also used to make ice cream. Do you know why? Read the article at the
following URL to find out, and then answer the questions below.

http://science.howstuffworks.com/nature/climate-weather/atmospheric/road-salt.htm

1. Describe how salt melts road ice.


2. Make a table, using data in the article, to show how adding salt to water changes its freezing point.


3. Explain why salt is used to make ice cream.

Review

1. Define freezing.


2. What happens to the particles of matter when it changes from a liquid to a solid?


3. What is the freezing point of a substance? What is the freezing point of water?

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