Phase Changes in Water

AIM: How does the Atmosphere store energy?

• Water exists on Earth in three states: solid (ice), liquid, and gas (water vapor)

• These “states of matter” can also be called “phases of matter”

• How do temperatures on our planet allow us to experience all three states of matter?

The Water Cycle!

• When water changes from one phase to another, a great deal of energy is involved

Energy gained – melt and vaporize

Energy released – condense and freeze

Notice temperature does not increase or decrease during a phase change.

• We call this latent heat = hidden energy that is absorbed or released when matter changes state

• A type of potential energy required to rearrange molecules only – not change temperature.

Animation

How do we measure energy?

• Scientists use joules (J) to measure energy• Named for the scientist who discovered that heat is

a form of energy

• ***Notice – more energy to boil (vaporize) and condense than to melt or freeze

James Prescott Joule

Specific Heat

• Different substances absorb different amounts of energy as their temperatures change…WHY?

• The reason is because they have different specific heats = the energy needed to raise the temperature of 1 gram of a substance 1C, without changing its state

• The higher the specific heat of a substance, the more energy needed to raise its temperature

• For example, it takes about 33 times as much energy to heat 1 g of water at 1C than it takes to hear 1 g of lead at 1C (the same amount of substance at the same temperature)