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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 .
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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. L H
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?)