Prentice Hall ©2004 Partial Pressure-Intro Mixture of Ar and H 2 H2H2 Ar Consider these boxes, all the same V and T:  If P is 3 atm in the H 2 box, what is P in the Ar box? P Ar = _____ P H2 = 3 atm 6 atm  And what would be the pressure if the two gases were put into the same box (at same V and T)? P total = _____9 atm  If P is 3 atm in the H 2 box, what is P in the Ar box? (Hint: there are twice as many particles)

Prentice Hall ©2004 Chapter 09Slide 2 Partial Pressures (in Gas Mixtures) The partial pressure of a gas A (P A ) is the pressure that Gas A would exert if it were the only gas in the vessel. Consider a box with volume V box with two gases in it, A and B, and at given temperature, T. n tot = PAPA PBPB P tot =+ n A + n B

Prentice Hall ©2004 Chapter 09Slide 3 Back to Earlier Example Mixture of Ar and H 2 P total = P H2 + P Ar = 3 atm + 6 atm = 9 atm

Prentice Hall ©2004 Copyright © Houghton Mifflin Company. All rights reserved.5–45–4 Figure 5.12, Zumdahl The Partial Pressure of each Gas in a Mixture of Gases in a Container Depends on the Number of Moles of that Gas

Prentice Hall ©2004 Chapter 09Slide 5 Dalton’s Law of Partial Pressures05 For a two-component system, the moles of components A and B can be represented by the mole fractions (X A and X B ). NOTICE: X A + X B = 1

Prentice Hall ©2004 Chapter 09Slide 6 Dalton’s Law of Partial Pressures06 Mole fraction is related to the total pressure by: On a humid day in summer, the mole fraction of gaseous H 2 O (water vapor) in the air at 25°C can be as high as Assuming a total pressure of atm, what is the partial pressure (in atm) of H 2 O in the air?

Prentice Hall ©2004 Chapter 09Slide 7 Dalton’s Law of Partial Pressures moles of Ne and 3.0 moles of Ar were placed in a 40.0 L container at 25 o C. What are the partial pressures of each gas and the total pressure?

Prentice Hall ©2004 Chapter 09Slide 8 Dalton’s Law of Partial Pressures02 A sample of natural gas contains 6.25 moles of methane (CH 4 ), moles of ethane (C 2 H 6 ), and moles of propane (C 3 H 8 ). If the total pressure of the gas is 1.50 atm, what are the partial pressures of the gases?

Prentice Hall ©2004 Chapter 09Slide 9 Dalton’s Law of Partial Pressures03 Hydrogen gas generated when calcium metal reacts with water is collected at 30°C and a pressure of 988 mm Hg. The volume collected is 641 ml. What is the mass (in grams) of the hydrogen gas obtained? The pressure of the water vapor at 30°C is 32 mm Hg. 760 mm Hg = 1.00 atm

Prentice Hall ©2004 Chapter 09Slide 10 Graham’s Law Diffusion is the mixing of different gases by random molecular motion and collision. Effusion is when gas molecules escape without collision, through a tiny hole into a vacuum.

Prentice Hall ©2004 Chapter 09Slide 11 Graham’s Law03 For two gases at same temperature and pressure: ( Again, “Big guys move more slowly at the same T!”) What are the relative rates of diffusion of the three naturally occurring isotopes of neon: 20 Ne, 21 Ne, and 22 Ne?