Kinetic Theory

Law vs Theory

Law: a mathematical rule (ex: ideal gaw law)
Theory: a possible explanation (ex: kinetic molecular theory is an explanation for the ideal gas law)

4 postulates of kinetic molecular theory

- volume of gas molecules is negligible
- pressure is caused by collisions btwn particles & sides of container
- particles exert no forces on each other
- temp is proportional to avg KE

Postulate: Volume of gas molecules is negligible

- usually true b/c atoms are very small and in a gas, they're very far apart

- not always true because atoms do have some volume

Postulate: Pressure is caused by collisions btwn particles & sides of container

- always true
- factors that affect the # of collisions:
* volume = volume decreases, collision frequency increases
* moles = moles increase, collisions increase in frequency
* temp = temp increases, collision frequency & force increases

Postulate: Particles exert no forces on each other

- closest to true under the following conditions:

* high temp

* lower pressure

* low intermolecular forces

Postulate: Temp is proportional to avg KE

- KE = 1/2mv^2
- particles in same sample have different speeds

Maxwell-Boltzmann Distribution

- shows the distributions of speeds
- peak represents average, which is proportional to temp

Same gas, diff. temps

the area under the curve must be the same @ all temps

Same temp, diff gases

since KE=1/2mv^2, smaller atoms move faster tha nlarger atoms at the same temp

Gases don't always ____________________. The MOST ideal behavior occurs when ___________________: that is, _________________________

behave ideally, KMT is true, high temp, low pressure, low IMF

Reasons for non-ideal behavior

atom size is significant -> causes pressure/volume to be HIGHER than predicted
IMF are significant -> causes volume/pressure to be LOWER than predicted