- Principles of Chemistry I: Honors
Fall 2013, Unique 52195
Lecture Summary, 19 November 2013
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, crms, of each molecule:
crms = (3RT/(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.
After working out a crms for our gas molecules, we now care about how often molecules collide with each other, not just with the walls of whatever container they are in. To do this, we worked out expressions for collision frequency (Z) and mean free path (lamba), which is the average distance a molecule travels between collisions. Both of these expressions contain information about the energy with which two molecules collide, which will be our key to understanding if they react in some interesting way.