1. Unit 7-Behavior of Gas Molecules Kinetic Molecular Theory Collision Theory of Gas Molecules

2. The behavior of gas molecules is understood by: ◦Applying the Kinetic Molecular Theory (Considering the motion and arrangement of molecules) ◦Applying Collision Theory of Gas Molecules

3. Kinetic Molecular Theory Kinetic Molecular Theory is based on the idea that particles of matter are always in motion. This applies to matter of all states including gas. Temperature measures the average kinetic energy of the particles in a sample of matter (Kinetic Energy = ½ mv 2 ).

4. Solids Particles are held in a relative fixed position to each other. They do vibrate in place. Therefore solids have definitive shape. Particles are very tightly packed and have extremely low kinetic energy. Attractive forces between particles are much more effective, compared to other states, due the reduced distance between them. Very organized Highest density Incompressible

5. Liquids Particles are in constant motion, not bound to a fixed position, and flow freely (fluid), hence, they have no shape. Particles are closer together with lower kinetic energy. Attractive forces between particles are more effective than in gases as a result of the reduced distance between them, causing liquids to have a fixed volume. More ordered than gases More dense than gases and less dense than solids Much less compressible than gases because liquid particles are already much closer together.

6. Gases Particles are in constant and random motion, not bound to a fixed position and flow freely (fluid), hence, gases have no shape. Particles are far apart and have high kinetic energy. Attractive forces between particles are far less effective due to the distance between the particles. As a result gases have no fixed volume. Disordered Low density Very compressible: lots of empty space.

7. Collision Theory of Gas Molecules Gas particles are in motion that is called Brownian motion – the best way to understand this motion is by calling it “random”. Collisions occur both with the boundary of the container and each other. The types of collisions are not perfectly elastic, but they are very close to elastic. Gas molecules will be attracted by both electrostatic and gravitational forces. The effects of this force is miniscule and is ignored. Gas molecules clearly have both mass and volume. The volume is so small, however, that each gas molecule is said to be a point without volume. Brownian Motion Brownian Motion Elastic Collision Intermolecular Forces

8. Ideal vs. Real Gas Ideal Gas ◦Motion is totally random ◦All collisions are elastic ◦Gas molecules do not have any intermolecular attraction ◦Gas molecules have no volume Real Gas ◦Motion is Brownian (almost but not quite random) ◦Collisions are not perfectly elastic ◦Gas molecules experience intermolecular attraction ◦Gas molecules have volume

9. Application to Gas Laws For all of the Gas Laws, the gases involved are assumed to be Ideal Gases. The difference between the behavior of Real and Ideal Gases is so small that except in very sensitive laboratory environments the difference can be ignored.