Properties of Water:

First, some definitions:

Joule:             A unit of energy (in this case, heat energy). Energy can be added to the water or removed from it.

Melting:          A phase change from solid to liquid. Heat energy must be added to cause melting.

Freezing:         A phase change from liquid to solid. Heat energy must be removed to cause freezing.

Vaporization:   A phase change from liquid to gas (water vapor). Heat energy must be added to cause water to vaporize (evaporate).

Condensation:  A phase change from vapor to liquid. Heat energy must be removed to cause condensation.

Density:           Mass/Volume. The density of water is 1g/ml at 3.98C. At this temperature water has it's minimum volume.
                       If water goes above OR below this temperature it will expand and become less dense. That's why ice floats!

Now some facts:

To melt water you must add 334 Joules of heat energy for every gram of ice (solid water) you want to melt.

To freeze water you must remove 334 Joules of heat energy for every gram of liquid water you want to freeze. The law of conservation of energy states: "Energy cannot be created nor destroyed" so if it's removed from the water it must go somewhere else. Often it just goes into the environment.

To vaporize water (make it evaporate) you must add 2260 Joules of heat energy for every gram of water you want to evaporate. Often this heat energy comes from the surface the water is on. If the water is on you, heat energy is transferred from you to the water causing it to evaporate. You lose the heat energy to the water making you cooler. This is why we perspire.

To make water vapor condense into liquid water you must remove 2260 Joules of heat energy for every gram of water that condenses. The energy that is removed usually enters the environment, the air where the condensation is occurring.

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