Chapter 12 Summary
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CHAPTER 12
Concentrating Matter
SUMMARY
KEY TERMS
number density
mole
Avogadro’s number
standard temperature and pressure (STP)
Avogadro’s law
ideal gas law
universal gas constant, R
humidity
partial pressure
relative humidity
Weather Update
Air pressure is directly related to the number density, or number of particles per unit of volume, of the gas molecules in a sample of air. Avogadro’s law states that two gas samples have the same number of molecules if temperature volume and pressure are the same. Avogadro’s law and the combined gas law together form the ideal gas law. The ideal gas law relates pressure, volume, temperature, and the number of moles by a proportionality constant. This constant, R, is called the universal gas constant.
The amount of water vapor in the air plays a big role in determining the weather. Water vapor density, or humidity, is dependent on air temperature and air pressure. When air is at 100% humidity, chances are it is raining, snowing, or densely foggy because the air is saturated with water molecules.
REVIEW EXERCISES
Question 12.1
1. Explain how you can determine the number of molecules in a breath of air.
Question 12.2
2. What type of weather do you predict if the relative humidity is 100%?
Question 12.3
3. Suppose that you have 22.4 L of helium, He, gas and 22.4 L of neon, Ne, gas at STP. Which of these statements is false?
Both samples contain the same number of atoms.
Both samples have the same number density, n/V.
The two samples have different masses.
The two samples have the same mass density, D.
Question 12.4
4. How many moles of nitrogen gas, N2(g), are contained in 2 liters at 350 K and 1.5 atm?
Question 12.5
5. Suppose the water vapor density is 1.5 mol/1000 L at a temperature of 35 ºC, and the maximum water vapor density at 35 ºC is 2.2 mol/1000 L. What is the relative humidity?