# Lec19 - Chapter Outline 1 Mole Fraction 2 Daltons Law of...

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LMALaput Chemistry 16 Lecture 19 Chapter Outline 1. Mole Fraction 2. Dalton’s Law of Partial Pressures 3. Stoichiometry involving gases 4. Kinetic Molecular Theory 5. Diffusion and Effusion 6. Graham’s Law of effusion 7. Deviations from the Ideal Gas Law DALTON’S LAW OF PARTIAL PRESSURES •Dalton’s law states that the pressure exerted by a mixture of gases is the sum of the partial pressures of the individual gases. P total = P A + P B + P C + . .... The partial pressure of each gas is equal to its mole fraction in the gaseous mixture times the total pressure of the mixture. •A part of any mixture can be described as a mole fraction, X A : X A = No. mol A / total no. mol of all components For gaseous mixture we can relate the mole fraction of each component to its partial pressure as follows. From the ideal gas equation, the number of moles of each component can be written as ° A = P A V/ RT, ° B = P b V / RT and so on And the total number of moles is ° TOTAL = P TOTAL V/RT Substituting into the definition of X A , ° A / ° A + ° B + … = P A V/RT ÷ P TOTAL V/RT X A = P A /P TOTAL Similarly, X B =P B /P TOTAL Example: If 100 mL of hydrogen, measured at 25.0° C and 3.00 atm pressure, and 100 mL of oxygen, measured at 25.0°C and 2.00 atm pressure, were forced into one of the containers at 25.0°C, what would be the pressure of the mixture of gases? P TOTAL = P H2 + P O2 3.00 atm + 2.00 atm = 5.00 atm The mole fraction of oxygen in the atmosphere is 0.2094. Calculate the partial pressure of O 2 in the air when the atmospheric pressure is 760 torr. (The partial pressure of each gas in a mixture is equal to its mole fraction in the mixture times the total pressure of the mixture) P O2 = X 02 × P TOTAL = 0.2094 × 760 torr = 159 torr Two tanks are connected by a closed valve. Each tank is filled with gas as shown and both tanks are held at the same temperature. We open the valve and allow the gases to mix. (a) After the gases mix, what partial pressure of each gas and what is the total pressure? (b) What is the mole fraction of each gas in the mixture? (a) For O 2 : P 2,O2 = P 1 V 1 /V 2 = 24.0 atm × 5.0 L / 8.0 L = 15.0 atm For N 2 : P 2,n2 = P 1 V 1 /V 2 = 32.0 atm × 3.0 L / 8.0 L = 12.0 atm P TOTAL = P 2,O2 + P 2,N2 = 15.0 atm + 12.0 atm = 27.0 atm (b) X O2 = P 2,O2 /P TOTAL = 15.0atm / 27.0 atm = 0.556 X N2 = P 2,N2 /P TOTAL = 12.0atm/27.0atm = 0.444 X O2 + X N2 should be equal to 1.

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## This note was uploaded on 07/09/2011 for the course SCIENCE 16 taught by Professor Uperg during the Spring '11 term at University of the Philippines Diliman.

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Lec19 - Chapter Outline 1 Mole Fraction 2 Daltons Law of...

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