1 / 14

Kinetic Theory of Gases

Kinetic Theory of Gases. Overview. Assume atomic picture of gases Simpler than solids/liquids, as interactions can be neglected Predict behavior E.g., relations between P and V , P and T … Test in lab experiments. Basic Picture. Gas consists of noninteracting particles

dante
Download Presentation

Kinetic Theory of Gases

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Kinetic Theory of Gases

  2. Overview • Assume atomic picture of gases • Simpler than solids/liquids, as interactions can be neglected • Predict behavior • E.g., relations between P and V, P and T… • Test in lab experiments

  3. Basic Picture • Gas consists of noninteracting particles • They move around randomly • Temperature corresponds to (average) speed of particles • Hotter  faster • Pressure a manifestation of collisions with container walls

  4. Basic Processes • Thermal expansion • Evaporation • A cooling process • Dissolving solids in liquids • Reaction rates • …

  5. More on Temperature • Prediction of kinetic theory: v is the average speed T is the temperature (in Kelvins) m is the mass of a gas particle kB is Boltzmann’s constant • Note that

  6. More on Pressure Weight W • Canonical example: container wih movable piston • P is the average force per unit area due to collisions with walls • Average because it fluctuates • Weight on piston balances this force, in equilibrium • W tells us P of gas

  7. Now change something… • E.g. add weight to the piston (T = const) • Forces out of equilibrium; piston drops • Collision rate increases until forces again balance • P has increased, V decreased • In fact, (Boyle)

  8. Computer Simulation • Allows changing N, W, v • Replaces tedious mathematical analysis • Explore all relations encoded in the Ideal Gas Law: PV = NkBT • Most of these relations are qualitatively obvious, some even quantitatively so!

  9. Another Example • Increase T keeping P fixed • Note: doubling T means increasing v by • Faster particles means harder collisions and more rapid • Piston rises, reducing collision rate • Equilibrium is restored • Model gives (constant P)

  10. Another Example • Increase N with P and T held fixed • More particles means more collisions, piston rises • Reduced collision rate restores equilibrium • In detail: (constant T, P)

  11. A slightly more complicated one… • Increase T with V and N held constant • Do it in two steps: • Increase T with P unchanged • Increase W to return V to its original value • Result: (constant V, N)

  12. Verifying the Predictions • These relations are simple predictions of atomic/kinetic theory • If they are found to hold in experiments, we gain confidence that the atomic picture is correct! • Several of them are easily checked in lab exercises

  13. Sample Exercises • Calculate v for gas at room temperature • It may take a few seconds for a smell to reach you from across a room, e.g. from a perfume bottle. What does this suggest about the path taken by the perfume particles?

  14. Reference • R. P. Feynman, et al., The Feynman Lectures on Physics, v. I (Addison Wesley, 1970)

More Related