Energy Associated With Evaporation and Condensation of Water In the Air
• Evaporation/vaporization takes a large amount of energy (to break hydrogen bonds). For example, water absorbs energy as it evaporates on your skin. Evaporation on the surface of a swimming pool will cool the water.
• Condensation releases a large amount of energy. For example, steam will burn you as it releases energy on your skin.
When water vapor in the air condenses to form water droplets in clouds it releases large amounts of energy.
As water evaporates into in air it cools the air and increases its humidity. Air at surface conditions can hold up to about 4% water before it becomes saturated and can not absorb more water. As humid air rises it expands and cools and if it reaches the saturation point clouds form as water is forced to condense. The condensation of water releases a lot of energy, heating the air and causing clouds to rise into larger thunderstorms clouds. The water released falls as precipitation.
Heat is absorbed as ice melts and it is released as it freezes. The latent heat of water is an important factor in weather systems and the stability of climates around the world.
|Figure 7.13. Cloud formation releases heat into the air.
|Figure 7.14. Melting ice absorbs heat from air and water