WWC - Evaporation Lesson

 

Evaporation

Water is unique on Earth as it is the only substance that naturally exists in all three states; solid, liquid, and gas.

Water (and all other substances) changes state due to energy being added or removed from it. As energy is added to liquid water, the individual molecules increase in kinetic energy until they are able to overcome the hydrogen bonding that held them together. The term used to describe individual molecules becoming gaseous from a liquid state is evaporation.

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When water evaporates, it leaves behind any substances that were previously dissolved in it. In fact, evaporation is an excellent way to purify water. Conversely, evaporation also is a method employed by people in many coastal communities to harvest minerals dissolved in salt water; by directing ocean water into shallow fields, salt farmers can extract sea salt through the evaporative power of the sun.

Many of the surface features on Earth are the result of minerals being dissolved in water and then later being deposited as the water evaporated. Halite (also known as rock salt) is found in large, inland quarries due to ancient inland seas that eventually evaporated, leaving the salt behind.

Some crystalline minerals - including quartz and its variations - are the result of this same process - water containing quartz molecules evaporates, leaving the quartz molecules behind.

Many fossils are also the result of evaporation - minerals dissolved in groundwater gradually replace the decaying organic molecules of buried bones and vegetation as the water in the ground evaporates.

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