Unit 3, Lessons 17 and 18

Lesson 17:

This unit tacked on another gas law to the three we've already learned about. It's called the ideal gas law, and it's described by this formula!:

PV = nRT

Check my summary for lesson 16 to remember what the letters stand for. This equation is helpful in finding almost anything you need and is closely associated with STP: standard temperature and pressure. Typically we use the ideal gas law to find out the volume or or the number of moles present in a sample of gas.

Problems:

3.) How many moles of hydrogen, H2, gas are contained in a volume of 2 L at 280 K and 1.5 atm?

PV = nRT

(1.5)(2) = n(0.082)(280)

3 = n(22.96)

n = 0.13 mol, there are 0.13 moles of hydrogen in his sample.

Lesson 18:

Humidity is defined as the amount of water present in an air (see: Florida). Humidity increases or decreases by evaporating from a larger body of water or by condensing onto a solid object, such as a glass of ice water (why glasses of tea "sweat"). The total number of moisture in the air is called relative humidity and cannot exceed 100%, but can be determined by finding the difference between the readings on a dry-bulb and wet-bulb thermometer. Warm air can hold more water than cold air, which explains why clouds form on cold days.

Problems:

1.) What does humidity measure? The amount of water present in the air.