31_562ln08

31_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

Info iconThis preview shows pages 1–4. Sign up to view the full content.

View Full Document Right Arrow Icon
MIT OpenCourseWare http://ocw.mit.edu 5.62 Physical Chemistry II Spring 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
5.62 Spring 2008 Lecture #31 Page 1 Kinetic Theory of Gases: Mean Free Path and Transport The mean free path λ . The mean free path is the average distance a particle traverses before it experiences a collision. In Lecture #31 we determined the average collision frequency for a particle, Z. The mean time between collisions is simply Z -1 . If the mean speed of a particle is v then the mean free path is ! = v Z . As a result, for like particles we find the mean free path equal to: ! = 1 2 "# d 2 . This is an important and interesting result. For a dilute hard sphere gas, the mean free path depends only on density; it is independent of temperature. However, if the particles had an attractive or repulsive potential between them, the mean free path would depend on T. Typical values at 300K for O 2 d = 0.361 nm π d 2 = 41Å 2 Z Z TOT / V λ 1 bar 6.2 × 10 9 coll s –1 7.6 × 10 34 coll m –3 s –1 7.1 × 10 –8 m (10 –6 in) 10 –6 bar 6.2 × 10 3 coll s –1 7.6 × 10 22 coll m –3 s –1 7.1 × 10 –2 m (3 in) Why is Z proportional to ρ and Z TOT to ρ 2 ? The effusion picture described in Lecture #31 assumed that no collisions occur when molecules pass through a hole of area A and thickness d. This means that it is necessary to assume that d λ . If this is condition is not satisfied, the description of gas escaping from the vessel must include collisions and transport phenomena. The probability of a particle traveling a distance r before experiencing a collision is revised 4/24/08 3:49 PM
Background image of page 2
5.62 Spring 2008 Lecture #31 Page 2 p(r) r p(r) = ! e "! r 0 < r < # Is this probability distribution normalized? What are
Background image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 4
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 11/27/2011 for the course CHEM 5.43 taught by Professor Timothyf.jamison during the Spring '07 term at MIT.

Page1 / 6

31_562ln08 - MIT OpenCourseWare http:/ocw.mit.edu 5.62...

This preview shows document pages 1 - 4. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online