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Heat, Temperature, and Thermal Energy Transfer

Define heat and temperature and convert between temperature scales

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Kinetic Theory

Kinetic Theory

Credit: Laura Guerin
Source: CK-12 Foundation
License: CC BY-NC 3.0

Describing gases in terms of pressure, temperature and volume is actually a macroscopic description of what is happening on the microscopic level. By describing gases in terms of the mass and speed of its molecules, you are using what is known as the kinetic theory of gases.

Why It Matters

  • Watch the video below on kinetic theory: 


  • The kinetic theory describes a gas as being made up of a large number of atoms or molecules that have random motion. By taking into account the motion of the atoms, their velocities and their masses, the kinetic theory has been able to accurately describe macroscopic properties such as pressure, temperature, volume and many other quantities. Compared to solids, these atoms or molecules in a gas are separated by distances that are much greater than their diameters. These distances are so great, that the forces between them are considered 0 or negligible.
  • The importance of the kinetic theory and its applications can be understood when looking at the experiments that were done during WWII. The kinetic theory is the basis for diffusion, where diffusion is described as the random motion of particles/atoms through space. Diffusion was one of the methods that were used to help create the materials for the atomic bomb. In the diffusion process that was used, uranium-235 flowed through porous membranes faster than uranium-236.
  • Credit: US government DOD and/or DOE photograph
    Source: http://en.wikipedia.org/wiki/File:Little_boy.jpg
    License: CC BY-NC 3.0

    Difussion was used to help create atomic weapons [Figure2]

Can You Apply It?

Using the information provided above, answer the following questions.

  1. If effusion is described as the process where gas molecules exit a container through a small hole, which would expect to have a greater chance of leaving first: a lighter atom or a heavier atom?
  2. What would the kinetic theory of gases say about the average temperature of a gas?
  3. How does kinetic theory explain why adding heat to a gas that is in a container causes the temperature of the gas to increase?

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Image Attributions

  1. [1]^ Credit: Laura Guerin; Source: CK-12 Foundation; License: CC BY-NC 3.0
  2. [2]^ Credit: US government DOD and/or DOE photograph; Source: http://en.wikipedia.org/wiki/File:Little_boy.jpg; License: CC BY-NC 3.0

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