Download Presentation
Kinetic Theory

Loading in 2 Seconds...

1 / 10

# Kinetic Theory - PowerPoint PPT Presentation

Kinetic Theory. Microscopic Analysis. The behavior of a gas should be described by the molecules. The gas consists of a large number of identical particles of mass m . The particles have negligible size and no internal structure.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
Download Presentation

## PowerPoint Slideshow about ' Kinetic Theory' - fionan

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.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript

### Kinetic Theory

Microscopic Analysis
• The behavior of a gas should be described by the molecules.
• The gas consists of a large number of identical particles of mass m.
• The particles have negligible size and no internal structure.
• The particles are moving in random dirctions with speeds independent of direction
• Collisions between particles and with the walls are perfectly elastic.
Collision Force
• Follow a collision with a wall perpendicular to x.
• Particle has mass m and a velocity vx.
• Strike the wall: Dt = 2L/vx.
• Impulse: Dp = 2mvx.
• The force from one particle:

L

Fx

v

m

Pressure Force
• The pressure on the wall comes from all the particles.
• The volume is V = AL.
• Find the value for N particles.

L

A

Three Dimensions
• The pressure come from all three dimensions, and is equal in all three.
• Relate the pressure to the average speed.

V

P

N

Theory Match
• The expression from a particle level relates the average kinetic energy.
• This almost matches the ideal gas law.

V

P

N

Temperature as Energy
• For the particle-level theory to match the experimental law we equate them.
• This is kinetic theory.
• Temperature measures the average kinetic energy.
What is the average energy of an air molecule at room temperature (293 K)?

What is average speed for a nitrogen molecule (28 g/mol)?

Energy directly relates to temperature.

(3/2)kT = 6.07 x 10-21 J.

To get the speed requires the mass.

m = (0.028 kg/mol) / (6.022 x 1023 /mol) = 4.65x10-26 kg

Average Energy
Distribution of Speeds
• Kinetic theory used the average speed.
• Actual atoms fall into a range of speeds.
• The Maxwell-Boltzmann distribution describes the probability of a molecule having a particular speed.
Real Gases
• The assumptions for kinetic theory are approximately true.
• Non-zero molecular size
• Non-zero force between molucules
• For the Van der Waals force in air, the effect is about 1% difference from an ideal gas.

next