University College - Chemistry Chem 112A Lecture Notes - Lecture 1: Gas Constant, Ideal Gas Law
13 Dec 2016
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20 January 2016
Lecture 1: Kinetic Theory of Gases
Equation of the Day:
I. Kinetic Theory and Maxwell-Boltzman
A. Kinetic Theory of Gases
1. A theory that looks at a gas as a collection of individual molecules with velocities,
kinetic energies, and momenta and analyzes the physics of those molecules
a. Allows us to empirically to determine the ideal gas law: PV=nRT
2. 4 Postulates of the kinetic theory:
a. The gas consists of a large number of identical molecules separated by distances
that are great compared to their sizes
b. The gas molecules are constantly moving in random directions with a distribution
of speeds
c. The molecules can collide elastically with each other (they bounce off with no
loss of kinetic energy), but they exert no forces on one another between collisions
d. The collisions of molecules with the walls of the container are also elastic (no loss
of KE during a collision)
3. Velocity (v) is a vector quantity which includes both speed (v) and the direction of
motion
a. v2 = vx2 + vy2 + vz2
B. Maxwell-Boltzman Distribution
1. Gas molecules following the 4 postulates of the kinetic theory (aka behaving ideally),
will show a Maxwell-boltzman speed distribution
2. Modeled by:
a. T is the absolute temperature (in Kelvin, °C + 273 = K)
b. v is the speed of the molecule
c. KB is the Boltzman constant = R/NA
• R (universal gas constant), NA = Avogadro’s number
• KB = 1.38x10-23 J/K
d. m is the mass of the molecule
3. Visualized:
a. Total area under the graph = 1
b. If you create a section between two speeds (v1 and v2) the shaded area would
represent the fraction of molecules with speeds between v1 and v2
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