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Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE Chapter 9 Gases: Their Properties and Behavior John E. McMurry Robert C. Fay CHEMISTRY.

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Presentation on theme: "Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE Chapter 9 Gases: Their Properties and Behavior John E. McMurry Robert C. Fay CHEMISTRY."— Presentation transcript:

1 Lecture Notes Alan D. Earhart Southeast Community College Lincoln, NE Chapter 9 Gases: Their Properties and Behavior John E. McMurry Robert C. Fay CHEMISTRY Copyright © 2008 Pearson Prentice Hall, Inc.

2 Gases and Gas Pressure © 2012 Pearson Education, Inc. Chapter 9/2 Gas mixtures are homogeneous and compressible.

3 Gases and Gas Pressure © 2012 Pearson Education, Inc. Chapter 9/3 Pressure: Unit area Force

4 Pressure Imbalance in Ear Tro, Chemistry: A Molecular Approach4 If there is a difference in pressure across the eardrum membrane, the membrane will be pushed out – what we commonly call a “popped eardrum.”

5 Gases and Gas Pressure © 2012 Pearson Education, Inc. Chapter 9/5 Barometer Pa torr mm Hg atm bar Units

6 Gases and Gas Pressure © 2012 Pearson Education, Inc. Chapter 9/6 (exact) Conversions 1 torr = 1 mm Hg 1 atm = 101 325 Pa (exact)1 atm = 760 mm Hg (exact)1 bar = 1 x 10 5 Pa

7 Gases and Gas Pressure

8 The Gas Laws Chapter 9/8 Ideal Gas: A gas whose behavior follows the gas laws exactly. The physical properties of a gas can be defined by four variables: Ppressure Ttemperature (calculation must be in Kelvin) Vvolume nnumber of moles

9 The Gas Laws Boyle’s Law  V P 1 (constant n and T)

10 The Gas Laws Boyle’s Law  V P 1 (constant n and T)

11 The Gas Laws © 2012 Pearson Education, Inc. Chapter 9/11 P initial V initial = P final V final Boyle’s Law  V P 1 (constant n and T) PV = k

12 Boyle’s Law and Diving since water is denser than air, for each 10 m you dive below the surface, the pressure on your lungs increases 1 atm at 20 m the total pressure is 3 atm Tro, Chemistry: A Molecular Approach12 if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs

13 Examples Calculate the volume of a sample of a gas at 5.75 atm if it occupies 5.14 L at 2.49 atm. (Assume constant temperature)

14 The Gas Laws Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 9/14 Charles’ Law V  T (constant n and P) = k T V = T final V final T initial V initial

15 The Gas Laws Charles’s Law V  T (constant n and P)

16 The Gas Laws © 2012 Pearson Education, Inc. Chapter 9/16 = k T V = T final V final T initial V initial Charles’s Law V  T (constant n and P)

17 Examples A sample of argon gas that originally occupied 14.6 L at 25.0 o C was heated to 50.0 o C at constant pressure. What is its new volume?

18 The Gas Laws Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 9/18 Avogadro’s Law V  n (constant T and P) = k n V = n final V final n initial V initial

19 Examples Consider two samples of nitrogen gas (composed N 2 molecules). Sample 1 contains 1.5 mol of N 2 and has a volume of 36.7 L at 25.0 o C and 1 atm. Sample 2 has a volume of 16.0 L at 25.0 o C and 1.0 atm. Calculate the number moles of N 2 in sample 2

20 The Ideal Gas Law Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 9/20 =Avogadro’s Law: P initial V initial = P final V final Boyle’s Law: n final V final n initial V initial Charles’ Law: = T final V final T initial V initial Summary If the systems is disturbed by one of the four variables: O, T, n then consider the following changes

21 Combine Gas Law is an expression obtained by mathematically combining Boyle’s and Charles’ law P 1 V 1 = P 2 V 2 @ constant n T 1 T 2 can predict P, V or T when condition is changed

22 Examples Suppose we have a 0.240 mol sample of ammonia gas at 25.0 o C with a volume of 3.5 L at a pressure of 1.68 atm. The gas compressed to a volume of 1.35 L at 25.0 o C. Use the combined gas law to calculate the final pressure.

23 The Ideal Gas Law Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 9/23 PV = nRT Standard Temperature and Pressure (STP) for Gases Ideal Gas Law: P = 1 atm T = 0 °C (273.15 K) R is the gas constant and is the same for all gases. R = 0.082058 K mol L atm

24 Examples What volume is occupied by 25.7 g of carbon dioxide gas at 25 o C and 371 torr? A 0.250 mol sample of argon gas has a volume of 9.00L at a pressure of 875 mmHg. What is the temperature (in o C) of the gas?

25 The Ideal Gas Law Copyright © 2008 Pearson Prentice Hall, Inc. Chapter 9/25 Is there a mathematical relationship between P, V, n, and T for an ideal gas?

26 The Ideal Gas Law © 2012 Pearson Education, Inc.Chapter 9/26 = 22.41 LV = P nRT = What is the volume of 1 mol of gas at STP ? (1 atm) (1 mol)0.08206 K mol L atm (273.15 K)

27 examples A sample of nitrogen gas has a volume of 1.75 L at STP. How many moles of N 2 are present?

28 Example Sodium peroxide (Na 2 O 2 ) is used to remove carbon dioxide from (and add oxygen to) the air supply in spacecrafts. It works by reacting with CO 2 in the air to produce sodium carbonate (Na 2 CO 3 ) and O 2. 2 Na 2 O 2 (s) + 2 CO 2 (g)  2 Na 2 CO 3 (s) + O 2 (g)


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