1. Water in the Atmosphere
Chapter 2.4
Pages 61-66

2. The Water Cycle
A. Evaporation - is the process by which water molecules in a liquid escape into air as water vapor
Requires energy (Endothermic) to break the water molecules apart
Will absorb heat energy from nearby particles.

3. The Water Cycle
B. Condensation- The process by which a gas, such as water vapor, changes to a liquid, such as water
Releases heat energy (Exothermic)
Will give heat energy to nearby particles.

4. The Water Cycle
C. Precipitation - rain, snow, sleet fall from clouds to the surface
D. Ground Water - water moves through the ground back to bodies of water
E. Run-off - water flows on the surface towards oceans, rivers, lakes and streams.

5. Humidity Humidity - A measure of the amount of water vapor in the air
Relative Humidity - The percentage of water vapor in the air (the actual amount compared to the maximum amount that the air can hold) at that temperature.

6. Relative Humidity Problems:
Air that is15°C Holds a maximum of 10 grams of water vapor.
What is the relative humidity if 8g of water vapor are in the air?
8 / 10 = 0.8 or 80% relative humidity
If the air is holding 3.5g of water vapor, what is the relative humidity?
3.5 / 10 = 0.35 or 35% relative humidity

7. L H Relative Humidity Depends on the temperature. Why?
Warm air is less dense
Has more room to hold water vapor
Cold air is more dense
Has less space to hold water vapor. L H

8. Measuring Humidity
Psychrometer - An instrument used to measure relative humidity, consisting of a wet-bulb thermometer, and a dry-bulb thermometer.

9. Relative Humidity
If the relative humidity is high, will there be much of a temperature difference between the thermometers and why?

10. Dew Point Dew Point - The temperature at which condensation begins
If the temperature = dew point…
Relative Humidity =
100%

11. Exit Pass
Explain why Evaporation takes in or gives off heat (Is evaporation Endo or Exothermic and why?)