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*Get out your homework to be checked for completion *Go over homework problems *Humidity *

1. How many calories are needed to change 50. 0 grams of ice at -15. 0 °C to steam at 120. 0 °C? 2. Calculate the number of calories given off when 32. 0 grams of steam cools from 110. 0 °C to ice at 40. 0 °C. 3. Calculate the calories released when 10. 0 g of steam at 120. 0 °C are converted into ice at minus 20. 0 °C. 4. Calculate the calories required to change 10. 0 g of ice at -10. 0˚C to 10. 0 g of steam at 110. 0˚C.

HUMIDITY The amount of water vapor in the air

Relative Humidity = Actual amount of water vapor in the air Amount the air is capable of holding

Actual amount of water vapor in the air Mixing Ratio mass of water vapor (grams) mass of dry air (kilograms)

Relative Humidity = mixing ratio Actual amount of water vapor in the air Amount of water vapor the air is capable of holding

Amount of water vapor the air is capable of holding Saturation Mixing Ratio When the mixing ratio = 100%

How near the air is to saturation Relative Humidity = mixing ratio Amount of water vapor the air is capable of holding saturation mixing ratio

So why is it called “Relative” humidity? It’s relative to the TEMPERATURE Look at the table at the top of page 481 in your book

Amount of Water Vapor Needed to Saturate a Kilogram of Air at Various Temperature (°C) Water Vapor Content at Saturation (g) -20 0. 75 -10 2 0 3. 5 5 5 10 7 15 10 20 14 25 20 30 26. 5

Sample Problem: If the temperature is 25°C and there are 10 grams of water vapor per 1 kg of air in the atmosphere, what is the relative humidity? 50%

Sample Problem: If the relative humidity is 75% and the temperature is 25°C, how many grams per kilogram of water vapor is currently in the atmosphere?

Practice Problem: If the relative humidity is 37. 7% and there are 10 g/kg of water vapor in the atmosphere, what is the current temperature? Temperature (°C) Water Vapor Content at Saturation (g) 10 7 15 10 20 14 25 20 30 26. 5

The temperature at which a parcel of air becomes saturated Measures the actual moisture content of the air. Relative humidity measures how near the air is to saturation.