lecture notes alan d. earhart southeast community college lincoln, ne chapter 9 gases: their...
TRANSCRIPT
Lecture NotesAlan D. Earhart
Southeast Community College • Lincoln, NE
Chapter 9Gases: Their Properties and Behavior
John E. McMurry • Robert C. Fay
C H E M I S T R Y
Copyright © 2008 Pearson Prentice Hall, Inc.
© 2012 Pearson Education, Inc.Chapter
9/2
Gas mixtures are homogeneous and compressible.
© 2012 Pearson Education, Inc.Chapter
9/3
Pressure:Unit area
Force
Tro, Chemistry: A Molecular Approach 4
If there is a differencein pressure acrossthe eardrum membrane,the membrane will bepushed out – what we commonly call a “popped eardrum.”
© 2012 Pearson Education, Inc.Chapter
9/5
Barometer
Patorr
mm Hgatmbar
Units
© 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 105 Pa
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:
P pressure
T temperature (calculation must be in Kelvin)
V volume
n number of moles
Boyle’s Law
VP1
(constant n and T)
Boyle’s Law
VP
1(constant n and T)
© 2012 Pearson Education, Inc.Chapter
9/11
PinitialVinitial = PfinalVfinal
Boyle’s Law
VP
1(constant n and T)
PV = k
Boyle’s Law and Divingsince water is denser
than air, for each 10 m you dive below the surface, the pressure on your lungs increases 1 atmat 20 m the total
pressure is 3 atm
Tro, Chemistry: A Molecular Approach 12
if your tank contained air at 1 atm pressure you would not be able to inhale it into your lungs
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)
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/14
Charles’ LawV T (constant n and P)
= kT
V
=Tfinal
Vfinal
Tinitial
Vinitial
Charles’s Law
V T (constant n and P)
© 2012 Pearson Education, Inc.Chapter
9/16
= kT
V
=Tfinal
Vfinal
Tinitial
Vinitial
Charles’s Law
V T (constant n and P)
ExamplesA sample of argon gas that originally
occupied 14.6 L at 25.0oC was heated to 50.0oC at constant pressure. What is its new volume?
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/18
Avogadro’s Law
V n (constant T and P)
= kn
V
=nfinal
Vfinal
ninitial
Vinitial
ExamplesConsider two samples of nitrogen gas
(composed N2 molecules). Sample 1 contains 1.5 mol of N2 and has a volume of 36.7 L at 25.0oC and 1 atm. Sample 2 has a volume of 16.0 L at 25.0oC and 1.0 atm. Calculate the number moles of N2 in sample 2
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/20
=Avogadro’s Law:
PinitialVinitial = PfinalVfinalBoyle’s Law:
nfinal
Vfinal
ninitial
Vinitial
Charles’ Law: =Tfinal
Vfinal
Tinitial
Vinitial
SummaryIf the systems is disturbed by one of the four variables: O, T, n then considerthe following changes
Combine Gas Law is an expression obtained by
mathematically combining Boyle’s and Charles’ law
P1V1 = P2V2 @ constant n
T1 T2
can predict P, V or T when condition is changed
ExamplesSuppose we have a 0.240 mol sample of
ammonia gas at 25.0oC 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 25.0oC. Use the combined gas law to calculate the final pressure.
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 = 0.082058K mol
L atm
ExamplesWhat volume is occupied by 25.7 g of carbon
dioxide gas at 25oC 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 oC) of the gas?
Copyright © 2008 Pearson Prentice Hall, Inc.
Chapter 9/25
Is there a mathematical relationship betweenP, V, n, and T for an ideal gas?
© 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) 0.08206K mol
L atm(273.15 K)
examplesA sample of nitrogen gas has a volume of
1.75 L at STP. How many moles of N2 are present?
ExampleSodium peroxide (Na2O2) is used to remove
carbon dioxide from (and add oxygen to) the air supply in spacecrafts. It works by reacting with CO2 in the air to produce sodium carbonate (Na2CO3) and O2.
2 Na2O2(s) + 2 CO2(g) 2 Na2CO3(s) + O2(g)