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Ch 20: The Micro/Macro Connection
Chapter 20, Problem 20

By what factor does the rms speed of a molecule change if the temperature is increased from 10℃ to 1000℃?

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

RMS Speed

The root mean square (RMS) speed of gas molecules is a measure of the average speed of particles in a gas. It is calculated using the formula v_rms = √(3kT/m), where k is the Boltzmann constant, T is the absolute temperature in Kelvin, and m is the mass of a molecule. This concept is crucial for understanding how temperature affects molecular motion.
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Temperature and Kinetic Energy

Temperature is a measure of the average kinetic energy of the particles in a substance. As temperature increases, the kinetic energy of the molecules also increases, leading to higher speeds. This relationship is fundamental in thermodynamics and helps explain how changes in temperature influence molecular behavior.
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Absolute Temperature Scale

The absolute temperature scale, measured in Kelvin (K), is essential for calculations involving gas laws and molecular speeds. To convert Celsius to Kelvin, you add 273.15. Understanding this scale is necessary for accurately determining the RMS speed when temperatures are given in Celsius.
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Related Practice
Textbook Question
Uranium has two naturally occurring isotopes. ²³⁸U has a natural abundance of 99.3% and ²³⁵U has an abundance of 0.7%. It is the rarer ²³⁵U that is needed for nuclear reactors. The isotopes are separated by forming uranium hexafluoride, UF₆, which is a gas, then allowing it to diffuse through a series of porous membranes. ²³⁵UF₆ has a slightly larger rms speed than ²³⁸UF₆ and diffuses slightly faster. Many repetitions of this procedure gradually separate the two isotopes. What is the ratio of the rms speed of ²³⁵UF₆ to that of ²³⁸UF₆?
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Textbook Question
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.
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Textbook Question
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?
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Textbook Question
Dust particles are ≈ 10 μm in diameter. They are pulverized rock, with p ≈ 2500 kg/m³. If you treat dust as an ideal gas, what is the rms speed of a dust particle at 20℃?
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Textbook Question
The molecules in a six-particle gas have velocities v₁ = (20î ─ 30ĵ) m/s v₂ = (40î + 70ĵ) m/s v₃ = (─80î + 20ĵ) m/s v₄ = 30î m/s v₅ = (40î ─ 40ĵ) m/s v₆ = (─50î ─ 20ĵ) m/s Calculate (a) →vₐᵥ₉ , (b) vₐᵥ₉, and (c) vᵣₘₛ.
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Textbook Question
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?
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