Page 257 - Schaum's Outline of Theory and Problems of Applied Physics

242 KINETIC THEORY OF MATTER [CHAP. 20

20.9. How many moles of H atoms are present in 1 mol of water, H 2 O?
(a) 2 (c) 2
3
(b) 1 (d) 3
20.10. The mass of a nitrogen atom is 14 u. The number of moles of molecular nitrogen (N 2 ) in 56 g of nitrogen is
(a) 2 (c) 28
(b) 4 (d) 64
20.11. A gas sample at 200 K is heated until its temperature is 400 K. If the original average velocity of the gas molecules
was v, their new average velocity is
(a) v (c) 2v
√
(b) 2v (d) 4v
◦
20.12. The molecules of a gas at 10 C would have twice as much average KE at
◦
(a) 20 C (c) 566 C
◦
(b) 293 C (d) 859 C
◦
◦
20.13. An oxygen molecule has 16 times the mass of a hydrogen molecule. A sample of hydrogen gas whose molecules
have the same average KE as the molecules in a sample of oxygen at 400 K is at a temperature of
(a) 25 K (c) 1600 K
(b) 400 K (d) 6400 K

Supplementary Problems

20.1. The volume of a gas sample is enlarged. Why does the pressure the gas exerts decrease?

20.2. The temperature of a gas sample is raised. Why does the pressure the gas exerts increase?
20.3. When they are close together, molecules attract one another slightly. As a result, are gas pressures higher or lower
than expected from the ideal gas law?
3
20.4. (a) Find the relative humidity of air at 20 C whose water vapor density is 8 g/m . (b) What is its dew point?
◦
20.5. Air at 25 C has a dew point of 15 C. What is its relative humidity?
◦
◦
20.6. Find the mass of the propane molecule C 3 H 8 and that of the glucose molecule C 6 H 12 O 6 .

20.7. The atomic mass of copper is 63.54 u. Find the number of atoms present in 100 g of copper.
20.8. A gas sample at 0 C is heated until the average energy of its molecules doubles. What is its new temperature?
◦
20.9. A gas sample at 0 C is heated until the average velocity of its molecules doubles. What is its new temperature?
◦
20.10. At room temperature oxygen molecules have an average velocity of about 1000 mi/h. (a) What is the average velocity
of hydrogen molecules, whose mass is one-sixteenth that of oxygen molecules, at this temperature? (b) What is the
average velocity of sulfur dioxide molecules, whose mass is twice that of oxygen molecules, at this temperature?
20.11. Mercury is a gas at 500 C. (a) What is the average energy of mercury atoms at this temperature? (b) What is the
◦
average velocity of mercury atoms at this temperature? The mass of a mercury atom is 3.3 × 10 −25 kg.