2.20. Boiling http://www.ck12.org
Vaporization vs. Evaporation
Vaporization is easily confused with evaporation, but the two processes are not the same. Evaporation also changes
a liquid to a gas, but it doesn’t involve boiling. Instead, evaporation occurs when particles at the surface of a liquid
gain enough energy to escape into the air. This happens without the liquid becoming hot enough to boil.
Boiling Point
The temperature at which a substance boils and changes to a gas is called its boiling point. Boiling point is a physical
property of matter. The boiling point of pure water is 100°C. Other substances may have higher or lower boiling
points. Several examples are listed in theTable2.5. Pure water is included in the table for comparison.
TABLE2.5:Boiling Points
Substance Boiling Point (°C)
Hydrogen -253
Nitrogen -196
Carbon dioxide -79
Ammonia -36
Pure water 100
Salty ocean water 101
Petroleum 210
Olive oil 300
Sodium chloride 1413Q:Assume you want to get the salt (sodium chloride) out of salt water. Based on information in the table, how could
you do it?
A:You could heat the salt water to 101°C. The water would boil and vaporize but the salt would not. Instead, the
salt would be left behind as solid particles.
Q:Oxygen is a gas at room temperature (20°C). What does this tell you about its boiling point?
A:The boiling point of oxygen must be lower than 20°C. Otherwise, it would be a liquid at room temperature.
Summary
- Vaporization is the process in which a liquid boils and changes to a gas.
- Vaporization is easily confused with evaporation, but evaporation doesn’t involve boiling.
- The temperature at which a liquid boils and starts changing to a gas is called its boiling point. The boiling
point of pure water is 100°C.
Vocabulary
- vaporization: Process in which a liquid boils and changes to a gas.
Explore More
Read about boiling at the following URL, and then answer the questions below.