1. I. Water’s Changes of State 18.1 Water in the Atmosphere  A) Precipitation is any form of water that falls from a cloud.  1) When studying the ATM, H20 is the most important gas in the atmosphere.

2. 18.1 Water in the Atmosphere  B) Solid to Liquid 1) melting ice requires energy be transferred in the form of heat. 2) Latent heat = energy absorbed or released during a change in state.

3.  C) Liquid to Gas 1) Evaporation -changing a liquid to a gas. 2) Condensation where a gas changes to a liquid 18.1 Water in the Atmosphere

4.  D) Solid to Gas 1) Sublimation conversion of solid directly to gas without passing through the liquid state. 2) Deposition is the conversion of a vapor directly to a solid.

5. Changes of State

6. II. Humidity 18.1 Water in the Atmosphere  A) Humidity- amount of water vapor in air. 1) Air is saturated when it contains the maximum quantity of H2o vapor that it can hold at any given temperature and pressure.  B) Saturation

7. II. Humidity 18.1 Water in the Atmosphere 1) Relative humidity- is a ratio or % of the air’s actual water-vapor content -compared with the amount of water vapor air can hold at that temperature and pressure.  C) Relative Humidity

8. II. Humidity 18.1 Water in the Atmosphere 2) when the water-vapor content of air remains constant, lowering air temperature causes an increase in relative humidity, and raising air temperature causes a decrease in relative humidity.

9. Relative Humidity Varies with Temperature

10. II. Humidity 18.1 Water in the Atmosphere  D) Dew Point 1) the temperature to which a parcel of air would need to be cooled to reach saturation.

11. II. Humidity 18.1 Water in the Atmosphere A hygrometer is an instrument to measure relative humidity.  E) Measuring Humidity

12. II. Humidity 18.1 Water in the Atmosphere 2) A psychrometer is a hygrometer with dry- and wet- bulb thermometers. Evaporation of water from the wet bulb makes air temperature appear lower than the dry bulb’s measurement. The two temperatures are compared to determine the relative humidity.

13. Sling Psychrometer