# Class8 - So P f = P i V i/V f =(0.5(1(4 =0.125 atm For others P Ne = 0.1 atm = P Ar Total P = sum = 0.325 Maybe derive total = sum Temperature&

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The Gas Law & Kinetic Theory CHEM 107 A. Bengali Texas A&M University Qatar

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Postulates of Kinetic Theory ) Huge # of molecules ) Point masses, no volume ) No forces between molecules ) Constant, chaotic motion ) Elastic collisions
PV = nRT For ANY gas under appropriate conditions ± Low P, High T

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He 1.0 L 0.50 atm Ne 1.0 L 0.40 atm Ar 2.0 L 0.20 atm ± Which contains the most atoms? ± Which contains the most mass? All gases at T = 0 ° C
) Calculate # atoms and mass for one of the gases - He, 0.5 atm, 1 L, 0 ° C (273 K) n= PV RT = (0.5) (1) (0.0821) (273) = 0.022 mol = 1.3x10 22 atoms ) And 0.022 mol at 4 g/mol is 0.089 g

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Partial Pressure ) P exerted by a single component in a gas mixture ) “What the pressure would be if only that gas were present in the container”
He 1.0 L 0.50 atm Ne 1.0 L 0.40 atm Ar 2.0 L 0.20 atm ± Open valves, let equilibrate ± Find partial and total pressures All gases at T = 0 ° C

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Partial P problem ) Each gas has fixed n, R, T ) So PV = constant, or P i V i = P f V f ) For helium:P i =0.5 atm,V i = 1 L, V f =4L

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Unformatted text preview: ) So: P f = P i V i /V f = (0.5)(1)/(4) =0.125 atm ) For others: P Ne = 0.1 atm = P Ar ) Total P = sum = 0.325 ) Maybe derive total = sum? Temperature & Energy ) T is proportional to the average kinetic energy of the molecules in a gas ) Ideal gas: KE avg = (3/2)RT Temperature & Energy ) At a given T, different gases have SAME average kinetic energy ) Since KE = 1/2 mv 2 , different gases at same T have different speeds Molecular Speeds ) Average speed α (T/m) 1/2 ) Light or Hot → fast ) Heavy or Cold → slow ) Details given by Maxwell-Boltzmann distribution function Speed Distributions: Effect of Mass Speed Distributions: Role of T Both curves for N 2 . One is at T = 300 K and one is at T = 1000 K. Which is which? He 1.0 L 0.50 atm Ne 1.0 L 0.40 atm Ar 2.0 L 0.20 atm ± Which gas has highest avg. KE? ± Which has highest avg. speed? All gases at T = 0 ° C...
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## This note was uploaded on 03/29/2008 for the course CHEM 107 taught by Professor Generalchemforeng during the Spring '07 term at Texas A&M.

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Class8 - So P f = P i V i/V f =(0.5(1(4 =0.125 atm For others P Ne = 0.1 atm = P Ar Total P = sum = 0.325 Maybe derive total = sum Temperature&

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