Chapter 9 Gases: Their Properties and Behavior. Gases and Gas Pressure Gas mixtures are homogeneous...
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Transcript of Chapter 9 Gases: Their Properties and Behavior. Gases and Gas Pressure Gas mixtures are homogeneous...
Chapter 9Gases: Their Properties and Behavior
Gas mixtures are homogeneous and compressible.
Pressure:Unit area
Force
4
If there is a differencein pressure acrossthe eardrum membrane,the membrane will bepushed out – what we commonly call a “popped eardrum.”
Barometer
Patorr
mm Hgatmbar
Units
(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
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)
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
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)
Charles’ LawV T (constant n and P)
= kT
V
=Tfinal
Vfinal
Tinitial
Vinitial
Charles’s Law
V T (constant n and P)
= 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?
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 1.0 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
=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.
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 25.0oC 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?
Determine the molar mass of a gas with a density of 1.905 g/L at 80.0oC
= 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?
What is the volume of 12.5 g of an methane (CH4) gas at STP