Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Chemistry FIFTH EDITION Chapter 5 Gases

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 Section 5.6 The Kinetic Molecular Theory of Gases Simple Model which attempts to explain the properties of an Ideal Gas. Before -- experimental point of view Now -- theory to explain the behavior.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 1.Volume of individual particles is  zero. 2.Collisions of particles with container walls cause pressure exerted by gas. 3.Particles exert no forces on each other. 4.Average kinetic energy  Kelvin temperature of a gas.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Figure 5.14 The Effects of Decreasing the Volume of a Sample of Gas at Constant Temperature Boyle’s Law: P V = kP = (nRT) 1/V

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Figure 5.15 The Effects of Increasing the Temperature of a Sample of Gas at Constant Volume P = (nR) T V

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Figure 5.16 The Effects of Increasing the Temperature of a Sample of Gas at Constant Pressure Charles’ Law: V = (n R) T P

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Figure 5.17 The Effects of Increasing the Number of Moles of Gas Particles at Constant Temperature and Pressure Avogadro’s Law: V = (RT) n P

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 The Meaning of Temperature Kelvin temperature is an index of the random motions of gas particles (higher T means greater motion.) ☻ See Exercise #78!! ☻ R = J/ K mole

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Root Mean Square Velocity Ave. Velocity of gas particles is a special kind of average. The square root of the average of the squares of the individual velocities of the gas particles. u rms = ( √ ū 2 ) = √(3RT/M)

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Root Mean Square Velocity u rms = √(3RT/M) (units are m/s) where M = mass of a mole of gas particles in kg R = J/mole K J = kg m 2 / s 2 Read Sample Exercise 5.19 on page 205.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Real gases experience a large # of collisions. A given particle will continuously change its course as a result of collisions with other particles, as well as with the walls of the container. See figure in next slide.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Figure 5.18 Path of One Particle in a Gas is typically very erratic.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Gas particles actually have a large range of velocities. Root mean square velocity gives us a feel for the average velocity of a gas particles. However, Most gas particles do not have this velocity.

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Figure 5.19 A Plot of the Relative Number of O 2 Molecules That Have a Given Velocity at STP u rms ≈ 500 m/s

Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Figure 5.20 A Plot of the Relative Number of N 2 Molecules That Have a Given Velocity at Three Temperatures