# chapter 5b - CHAPTER 5b The Properties of Gases 1 The...

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1 CHAPTER 5b The Properties of Gases 2 The Kinetic-Molecular Theory ± The basic assumptions of kinetic-molecular theory are: ± Postulate 1 ² Gases consist of discrete molecules that are relatively far apart. ² Gases have few intermolecular attractions. ² The volume of individual molecules is very small compared to the gas’s volume. (Gas molecules are infinitesimally small points.) ± Proof - Gases are easily compressible. 3 The Kinetic-Molecular Theory ± Postulate 2 ² Gas molecules are in constant, random, straight line motion with varying velocities. ± Proof - Brownian motion displays molecular motion.

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4 The Kinetic-Molecular Theory ± Postulate 3 ² Gas molecules have elastic collisions with themselves and the container. ² Total energy is conserved during a collision. ± Proof - A sealed, confined gas exhibits no pressure drop over time. 5 The Kinetic Model of Gases The kinetic model of gases regards gas molecules as infinitesimal small points that travel in straight lines until they undergo instantaneous collisions. 6 The Kinetic-Molecular Theory ± Postulate 4 ² The kinetic energy of the molecules is proportional to the absolute temperature. ² The average kinetic energies of molecules of different gases are equal at a given temperature. ± Proof - Brownian motion increases as temperature increases.
7 The Kinetic-Molecular Theory The gas laws that we have looked at earlier in this chapter are proofs that kinetic-molecular theory is the basis of gaseous behavior. ± Boyle’s Law ² P 1/V ² As the V increases the molecular collisions with container walls decrease and the P decreases. 8 The Kinetic-Molecular Theory ± Dalton’s Law ² P total = P A + P B + P C + . .... ² Because gases have few intermolecular attractions, their pressures are independent of other gases in the container. ± Charles’ Law ² V T ² An increase in temperature raises the molecular velocities, thus the V increases to keep the P constant. 9 The Kinetic-Molecular Theory ± The quantitative kinetic molecular model is clearly defined on pages 156 -160. Please take a moment to read through this quantitative description of the theory.

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10 The Kinetic-Molecular Theory ± Pressure as defined by kinetic energy of gas molecules is given by the following equation (derived on pages 158-159). Where: P = pressure of a gas N A = Avogadro’s number n = number of moles of gas m = mass of each gas particle V = volume of the container u 2 = the average of the squares of the velocities of the particles 2 2 () 2( ) 3 A mu kinetic energy energycaused by motion nN mu P V =  =   ½ ½ 11 The Kinetic-Molecular Theory ± The meaning of temperature.
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## This note was uploaded on 09/02/2009 for the course CH 301 taught by Professor Fakhreddine/lyon during the Fall '07 term at University of Texas at Austin.

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chapter 5b - CHAPTER 5b The Properties of Gases 1 The...

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