Prentice Hall © 2003Chapter 10

Prentice Hall © 2003Chapter 10 Look here tomorrow after Period 5 for a link for your class work from the Gas Laws Packet. These problems are good practice, but spend more time looking at the problems listed in the notes as well as the problem set problems to prepare for your test

Prentice Hall © 2003Chapter 10 Other information: Solve the questions listed in today’s notes after notes are completed. DO THE PROBLEM SET WITHOUT LOOKING AT THE ANSWERS 1 st There will be no board points for Chapter 10; There will be a bonus on the exam. Read the lab hand out by class time on Thursday. There will be time to ask/answer questions on Thursday while we are waiting for the lab to be completed.

Prentice Hall © 2003Chapter 10 Theory of moving molecules Assumptions: –Molecules in constant random motion –Volume of individual molecules is negligible –Intermolecular forces are negligible –Energy can be transferred between molecules, but total KE is constant at constant T –Average KE of molecules is proportional to T 10.7: Kinetic Molecular Theory

Prentice Hall © 2003Chapter 10 Amount of pressure depends on frequency and magnitude of molecular collisions Gas molecules have an average kinetic energy –Each molecule has a different energy Average KE increases with increasing T

Prentice Hall © 2003Chapter 10 As kinetic energy increases, the velocity of the gas molecules increases Root mean square speed, u, is the speed of a gas molecule having average kinetic energy Average kinetic energy, , is related to root mean square speed:

Prentice Hall © 2003Chapter 10 Kinetic Energy has a set value at a specified temperature Mathematically: 10.8: Molecular Effusion and Diffusion Molar mass in the denominator, so an increase in molar mass will decrease the u of the molecules R = This value of R allows u to have velocity units

Prentice Hall © 2003Chapter 10 Graham’s Law of Effusion Effusion is the escape of a gas through a tiny hole (a balloon will deflate over time due to effusion)

Prentice Hall © 2003Chapter 10 Consider two gases with molar masses M 1 and M 2. The relative rate of effusion is given by: Only those molecules that hit the small hole will escape through it The higher the root mean square speed (rms), the more likely a gas molecule will hit the hole Graham’s Law

Prentice Hall © 2003Chapter 10 Diffusion and Mean Free Path Diffusion of a gas is the spread of the gas through space Diffusion is faster for light gas molecules Diffusion is significantly slower than rms speed consider someone opening a perfume bottle: it takes a while to detect the odor, but rms speed at 25  C is about 1150 mi/hr Diffusion is slowed by gas molecules colliding with each other

Prentice Hall © 2003Chapter 10 Average distance traveled by a gas molecule between collisions is called mean free path Varies with pressure At sea level, mean free path is about 6  cm

Prentice Hall © 2003Chapter 10 Sample Problems # 67, 69

Prentice Hall © 2003Chapter 10 From the ideal gas equation, we have For 1 mol of gas, PV/RT = 1 for all pressures In a real gas, PV/RT varies from 1 significantly The higher the pressure the greater the deviation from ideal behavior 10.9: Real Gases: Deviations from Ideal Behavior

Prentice Hall © 2003Chapter 10 As the gas molecules get closer together, the intermolecular distance decreases attractive forces take over (real gas) Text, P. 394

Prentice Hall © 2003Chapter 10 As temperature increases, the gas molecules move faster and further apart more energy is available to break intermolecular forces Therefore, the higher the temperature, the more ideal the gas Text, P. 394

Prentice Hall © 2003Chapter 10 The assumptions in kinetic molecular theory show where ideal gas behavior breaks down: –the molecules of a gas have finite volume –molecules of a gas do attract each other

Prentice Hall © 2003Chapter 10 The van der Waals Equation Two terms are added to the ideal gas equation: correct for volume of molecules correct for intermolecular attractions The correction terms generate the van der Waals equation:

Prentice Hall © 2003Chapter 10 where a and b are empirical constants General form of the van der Waals equation: Corrects for molecular volume Corrects for molecular attraction

Prentice Hall © 2003Chapter 10 Text, P. 395

Prentice Hall © 2003Chapter 10 Sample Problem # 77