CH301H
- Principles of Chemistry I: Honors Fall 2011, Unique 51040 Lecture Summary, 10 November 2011 |

Kinetic
Model of Gasses:
Now that we know how ideal gasses behave, we have to know
how often and with what energy two molecules
collide. To do this, we imagined a box filled with
molecules moving in the x direction and
colliding with the walls of the box. By calculating
the total change in momentum that occurs with each
collision, we worked out an expression for the root mean
square speed, c, of each molecule:_{rms}c=
(3_{rms} RT/(FW))^{1/2}This is a remarkable result because it describes the kinetic energy of a molecule (through its velocity) in terms of constants ( 3, R, FW), and an easily
measured property, T. We also discussed the idea that at a given temperature, the above equation will only give us the average
velocity of all molecules in the system, but that
individual molecules have different velocities and
therefore different kinetic energy. The range
of velocities is given by the Maxwell-Boltzmann
distribution. Although we will not derive this
explicitly, the form of the equation tells us that the
distribution is asymmetric, with a long tail towards
higher velocities. This means that even at low
temperatures, there will always be a few molecules moving
at very high velocity, and thus capable of performing high
energy collisions. |