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Unformatted text preview: CHAPTER 14 THE IDEAL GAS LAW AND KINETIC THEORY CONCEPTUAL QUESTIONS ____________________________________________________________________________________________ 1 . REASONING AND SOLUTION a. Avogadro's number N A is the number of particles per mole of substance. Therefore, one mole of hydrogen gas (H 2 ) and one mole of oxygen gas (O 2 ) contain the same number (Avogadro's number) of molecules. b. One mole of a substance has a mass in grams that is equal to the atomic or molecular mass of the substance. The molecular mass of oxygen is greater than the molecular mass of hydrogen. Therefore, one mole of oxygen has more mass than one mole of hydrogen. ____________________________________________________________________________________________ 2 . REASONING AND SOLUTION Substances A and B have the same mass densities. Therefore, the mass per unit volume of substance A is equal to that of substance B. a. The mass of one mole of a substance depends on the molecular mass of the substance. In general, the molecular masses of substances A and B will differ, and one mole of each substance will not occupy the same volume; therefore, even though substances A and B have the same mass density, one mole of substance A will not have the same mass as substance B. b. Since the mass per unit volume of substance A is the same as the mass per unit volume of substance B, 1 m 3 of substance A has the same mass as 1 m 3 of substance B. ____________________________________________________________________________________________ 3 . REASONING AND SOLUTION A tightly sealed house has a large ceiling fan that blows air out of the house and into the attic. The fan is turned on, and the owners forget to open any windows or doors. As the fan transports air molecules from the house into the attic, the number of air molecules in the house decreases. Since the house is tightly sealed, the volume of the house remains constant. If the temperature of the air inside the house remains constant, then from the ideal gas law, PV = nRT , the pressure in the house must decrease. The air pressure in the attic, however, increases. The fan must now blow air from a lower pressure region to a higher pressure region. Thus, it becomes harder for the fan to do its job. ____________________________________________________________________________________________ 4 . SSM REASONING AND SOLUTION According to the ideal gas law (Equation 14.1), PV = nRT . Therefore, the pressure of a gas confined to a fixed volume is directly proportional to the Kelvin temperature. Therefore, when the temperature is increased, the pressure increases proportionally. The gas above the liquid in a can of hair spray is at a relatively high pressure. If the temperature of the can is increased to a sufficiently high temperature, the pressure of the confined gas could increase to a value larger than the walls of the can will sustain. The can 192 THE IDEAL GAS LAW AND KINETIC THEORY would then explode. Therefore, the label on hair spray cans usually contains the warning would then explode....
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- Spring '07