Problem 1
The mean free path of a molecule in a gas is 300 nm. What will the mean free path be if the gas temperature is doubled at (a) constant volume and (b) constant pressure?
Problem 3
A 1.0 m ✕ 1.0 m ✕ 1.0 m cube of nitrogen gas is at 20℃ and 1.0 atm. Estimate the number of molecules in the cube with a speed between 700 m/s and 1000 m/s.
Problem 5
Integrated circuits are manufactured in vacuum chambers in which the air pressure is 1.0 x 10-10 of Hg. What are (a) the number density and (b) the mean free path of a molecule? Assume T = 20℃.
Problem 7
A cylinder of nitrogen and a cylinder of neon are at the same temperature and pressure. The mean free path of a nitrogen molecule is 150 nm. What is the mean free path of a neon atom?
Problem 8
Eleven molecules have speeds 15, 16, 17, …, 25 m/s. Calculate (a) vavg and (b) vrms.
Problem 9
The molecules in a six-particle gas have velocities:
Calculate (a) , (b) , and (c) .
Problem 11
At 100℃ the rms speed of nitrogen molecules is 576 m/s. Nitrogen at 100℃ and a pressure of 2.0 atm is held in a container with a 10 cm x 10 cm square wall. Estimate the rate of molecular collisions (collisions/s) on this wall.
Problem 13
A cylinder contains gas at a pressure of 2.0 atm and a number density of 4.2 x 1025 m-3. The rms speed of the atoms is 660 m/s. Identify the gas.
Problem 18
The rms speed of molecules in a gas is 600 m/s. What will be the rms speed if the gas pressure and volume are both halved?
Problem 19
By what factor does the rms speed of a molecule change if the temperature is increased from 10℃ to 1000℃?
Problem 21
1.0 mol of argon has 3100 J of thermal energy. What is the gas temperature in °C?
Problem 22
Liquid helium boils at 4.2 K. In a flask, the helium gas above the boiling liquid is at the same temperature. What are (a) the mean free path in the gas, (b) the rms speed of the atoms, and (c) the average energy per atom?
Problem 26
The rms speed of the atoms in a 2.0 g sample of helium gas is 700 m/s. What is the thermal energy of the gas?
Problem 28
A 6.0 m ✕ 8.0 m ✕ 3.0 m room contains air at 20℃. What is the room's thermal energy?
Problem 29
The thermal energy of 1.0 mol of a substance is increased by 1.0 J. What is the temperature change if the system is (a) a monatomic gas, (b) a diatomic gas, and (c) a solid?
Problem 30
The vibrational modes of molecular nitrogen are 'frozen out' at room temperature but become active at temperatures above ≈1500 K. The temperature in the combustion chamber of a jet engine can reach 2000 K, so an engineering analysis of combustion requires knowing the thermal properties of materials at these temperatures. What is the expected specific heat ratio γ for nitrogen at 2000 K?
Problem 34a
2.0 mol of monatomic gas A initially has 5000 J of thermal energy. It interacts with 3.0 mol of monatomic gas B, which initially has 8000 J of thermal energy. Which gas has the higher initial temperature?
Problem 38b
Your calculator can't handle enormous exponents, but we can make sense of large powers of e by converting them to large powers of 10. If we write e = 10α, then eβ = (10α)β = 10αβ. What is the multiplicity of a macrostate with entropy S = 1.0 J/K? Give your answer as a power of 10.
Problem 40
A 75 g ice cube at 0℃ is placed on a very large table at 20℃. You can assume that the temperature of the table does not change. As the ice cube melts and then comes to thermal equilibrium, what are the entropy changes of (a) the water, (b) the table, and (c) the universe?
Problem 41
What is the entropy change of the nitrogen if 250 mL of liquid nitrogen boils away and then warms to 20℃ at constant pressure? The density of liquid nitrogen is 810 kg/m3.
Problem 43
2.0 mol of helium at 280℃ undergo an isobaric process in which the helium entropy increases by 35 J/K. What is the final temperature of the gas?
Problem 45
The pressure inside a tank of neon is 150 atm. The temperature is 25℃. On average, how many atomic diameters does a neon atom move between collisions?
Problem 46
Dust particles are ≈ 10 μm in diameter. They are pulverized rock, with ρ ≈ 2500 kg/m³. If you treat dust as an ideal gas, what is the rms speed of a dust particle at 20℃?
Ch 20: The Micro/Macro Connection