Water in the Atmosphere

Water in the Atmosphere

Chapter 2.4Pages 61-66

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.

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.

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.

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.

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

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.

HL

Measuring Humidity

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

Relative Humidity• If the relative

humidity is high, will there be much of a temperature difference between the thermometers and why?

Dew Point

• Dew Point - The temperature at which condensation begins

• If the temperature = dew point…• Relative Humidity = 100%

Exit PassExplain why Evaporation

takes in or gives off heat (Is evaporation Endo or

Exothermic and why?)