Download Water in the Atmosphere

Water in the
Atmosphere
Chapter 2.4
Pages 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.
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 Pass
Explain why Evaporation
takes in or gives off heat (Is
evaporation Endo or
Exothermic and why?)