Kinetic Molecular Theory

Kinetic Theory

Kinetic Molecular Theory Postulates of the Kinetic Molecular Theory of Gases 1.Gases consist of tiny particles (atoms or molecules) 2.These particles are so small, compared with the distances between them, that the volume (size) of the individual particles can be assumed to be negligible (zero). 3. The particles are in constant random motion, colliding with the walls of the container. These collisions with the walls cause the pressure exerted by the gas. 4. The particles are assumed not to attract or to repel each other. 5. The average kinetic energy of the gas particles is directly proportional to the Kelvin temperature of the gas

Model Gas Behavior All collisions must be elastic Take one step per beat of the metronome Container –Class stands outside tape box Higher temperature –Faster beats of metronome Decreased volume –Divide box in half More Moles –More students are inside box  Mark area of container with tape on ground.  Add only a few molecules of inert gas  Increase temperature  Decrease volume  Add more gas  Effect of diffusion  Effect of effusion (opening size)

Pressure - Temperature - Volume Relationship P T V Gay-Lussac’s P T  CharlesV T  P T V Boyle’s P 1V1V  ___

Pressure - Temperature - Volume Relationship P T V Gay-Lussac’s P T  CharlesV T  Boyle’s P 1V1V  ___ P n V

Pressure and Balloons A B = pressure exerted ON balloon A = pressure exerted BY balloon B When balloon is being filled: P A > P B When balloon is filled and tied: P A = P B When balloon deflates: P A < P B

When the balloons are untied, will the large balloon (A) inflate the small balloon (B); will they end up the same size or will the small balloon inflate the large balloon? Why? Balloon Riddle A B C

Kinetic Theory and the Gas Laws Dorin, Demmin, Gabel, Chemistry The Study of Matter, 3 rd Edition, 1990, page 323 (newer book)

Molar Volume Timberlake, Chemistry 7 th Edition, page 268

Volume and Number of Moles Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 413

A Gas Sample is Compressed Zumdahl, Zumdahl, DeCoste, World of Chemistry  2002, page 429

In a smaller container - molecules have less room to move. They hit the sides of the container more often. This causes an increase in pressure. As volume decreases: pressure increases. Changing the Size of the Container