Ch12_KMT

# Ch12_KMT - KINETIC MOLECULAR THEORY(KMT 1 Theory used to...

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Unformatted text preview: KINETIC MOLECULAR THEORY (KMT) 1 Theory used to explain gas laws. KMT assumptions are • Gases consist of molecules in constant, random motion. • P arises from collisions with container walls. • No attractive or repulsive forces between molecules. Collisions elastic. • Volume of molecules is negligible. Kinetic Molecular Theory Kinetic Molecular Theory u2 root mean square speed where u is the speed and M is the molar mass. • speed INCREASES with T • speed DECREASES with M Kinetic Molecular Theory 3 At the same T, all gases have the same average KE. As T goes up, KE also increases — and so does speed. Because we assume molecules are in motion, they have a kinetic energy. KE = _____________ At the same T, At the same T, ________________________ ________________________ As T goes up, KE also _____________ — and so does speed. 4 5 Maxwell’s equation 3RT M 2 Distribution of Gas Molecule Speeds Page 1 Velocity of Gas Molecules Molecules of a given gas have a Molecules speeds. range of range of 6 Velocity of Gas Molecules 7 8 GAS DIFFUSION AND EFFUSION Average velocity decreases with increasing mass. • diffusion is the gradual mixing of molecules of different gases. GAS DIFFUSION AND EFFUSION Graham’s law governs effusion and diffusion of gas molecules. Rate for A Rate for B M of B M of A Rate of effusion is Rate of effusion is inversely proportional inversely proportional to its molar mass. to its molar mass. Thomas Graham, 1805-1869. Professor in Glasgow and London. 10 Molecules effuse thru holes in a rubber balloon, for example, at a rate (= moles/time) that is • proportional to T • inversely proportional to M. Therefore, He effuses more rapidly than O 2 at same T. • effusion is the movement of molecules through a small hole into an empty container. Gas Diffusion relation of mass to rate of diffusion relation of mass to rate of diffusion •• HCl and NH33 diffuse HCl and NH diffuse from opposite ends from opposite ends of tube. of tube. •• Gases meet to form Gases meet to form NH44Cl NH Cl •• HCl heavier than NH 33 HCl heavier than NH •• Therefore, NH 44Cl Therefore, NH Cl forms closer to HCl forms closer to HCl end of tube. end of tube. Page 2 9 GAS DIFFUSION AND EFFUSION He 11 12 Using KMT to Understand Gas Laws Recall that KMT assumptions are • Gases consist of molecules in constant, random motion. • P arises from collisions with container walls. • No attractive or repulsive forces between molecules. Collisions elastic. • Volume of molecules is negligible. Avogadro’s Hypothesis and Hypothesis Kinetic Molecular Theory 13 14 Gas Pressure, Temperature, and Kinetic Molecular Theory P proportional to n Deviations from Ideal Gas Law • Real molecules have volume. • There are 16 Deviations from Ideal Gas Law 17 Account for volume of molecules and intermolecular forces with ( – Otherwise a gas could not become a liquid. P + n2 a ----2 V Deviations from Ideal Gas Law Measured P P + n2 a ----V2 ) Measured V = V(ideal) V - nb nRT vol. correction Measured V = V(ideal) Measured P intermol. forces V - nb nRT vol. correction intermol. forces Fig. 12.20 Page 3 15 P proportional to 1/V P proportional to T VAN DER WAAL’S EQUATION . intermolecular forces. Boyle’s Law and Kinetic Molecular Theory J. van der Waals, 1837-1923, Professor of Physics, Amsterdam. Nobel Prize 1910. Cl2 gas has a = 6.49, b = 0.0562 For 8.0 mol Cl 2 in a 4.0 L tank at 27 oC. P (ideal) = nRT/V = 49.3 atm P (van der Waals) = 29.5 atm 18 ...
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## This note was uploaded on 10/19/2011 for the course CHM 2210 taught by Professor Mcquade during the Fall '08 term at FSU.

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