1. Water’s Changes of State
Chapter 18
Water’s Changes of State
WATER is the most important gas when it relates to weather processes!
Who is Stan Hatfield and Ken Pinzke

2. Mr. Fetch's Earth Science Class
Moisture: Change of State
MELTING
Uses Heat
FREEZING
Gives off Heat
Sublimation
Deposition
EVAPORATION
Uses Heat
CONDENSATION
Gives off Heat
Energy is absorbed or released during a change in state. This is called LATENT HEAT.
Mr. Fetch's Earth Science Class

3. 18.1 What happens during a change of state?
•absorbed heat = molecules move apart
released heat = molecules move closer

4. 18.1 Water in the Atmosphere
Humidity
 Humidity is a general term for the amount of water vapor in air.
 Saturation
• When air contains the maximum amount of water vapor that it can hold at any given temperature and pressure.
• **Warm air can hold more water vapor than cold air!

5. Mr. Fetch's Earth Science Class
Warm air holds more moisture than cold air.
Mr. Fetch's Earth Science Class

6. 18.1 Water in the Atmosphere
Humidity
18.1 Water in the Atmosphere
 Relative Humidity
• Relative humidity is a ratio of the air’s actual water-vapor content compared with the amount of water vapor air can hold or capacity
RH = Actual content X 100
Maximum Capacity

7. What can change the relative humidity of air?
It can be changed by
adding or removing water vapor
If the water-vapor is kept constant
Temperature relative humidity
Temperature relative humidity

8. Relative Humidity

9. 18.1 What is Dew Point?  Dew Point
The temperature at which air is cooled to be full of water (saturated).
Water vapor turns to liquid
High dew points indicate moist air
Low dew points mean dry air.
Dew is particularly heavy on clear nights, when the earth cools rapidly. On cloudy nights, the cooling rate is slower.

10. Dew on a Spider Web
Makes no sense without caption in book

11. Measuring Humidity
A hygrometer is an instrument to measure relative humidity.
A psychrometer is a hygrometer with dry- and wet-bulb thermometers. Water evaporates from the wet bulb and the air temperature appears lower than the dry bulb. The two temperatures are compared to determine the relative humidity.

12. Sling Psychrometer
Makes no sense without caption in book