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UNIT 5: GAS AND ATMOSPHERIC CHEMISTRY11.2 & 11.3 Gas Laws
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CONTEXT
In a gas, the particles are very far apart This means that there is a lot of empty space
between them This makes gases compressible
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CONSIDER THIS…
What happens to the volume of a gas when you increase the pressure? Ex: press a syringe that is stoppered)
Why? Gases are compressible
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ANIMATION
http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_graph.html
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BOYLE’S LAW
In the 17th, Robert Boyle described this as “the spring in the air”
As pressure on a gas increases, the volume of the gas decreases proportionally, if temperature and amount of gas (moles) remain constant.
P α 1/V
PV = k
P1V1 = P2V2
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EXAMPLE PROBLEM
A 550 L weather balloon at 98 kPa is released from the ground and rises into the atmosphere. It is caught a later height and instruments indicate the air pressure is 75 kPa. What is the volume of the captured balloon?
P1=
V1=
P2=
V2=
98 kPa
550 L
75kPa
?
P1V1=P2V2
(98 kPa)(550L) = (75 kPa)(V2)V2= 719 L
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REAL LIFE APPLICATIONS
Scuba Diving As they dive down underwater, the pressure
increases volume? What happens to volume as you ascend in
water?
Ears popping!
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CHARLES’ LAW
Temperature and Volume
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ABSOLUTE ZERO This temperature is absolute zero, the
lowest possible temperature. A theoretical temperature at which matter
has no kinetic energy (volume of 0) and therefore transmit no thermal energy.
-273.15 ˚C
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TEMPERATURE SCALES
1˚C = 1 K ˚C = K - 273.15 K = ˚C + 273.15
Kelvin devised a new scale that would have no negative values
In this unit, we will ALWAYS use K
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CHARLES’ LAW
A direct relationship V α TV = kTVi = VfTi Tf
As the temperature of a gas increases, the volume increases proportionally, when pressure and amount of gas (moles) remains
constant.
Temperature (in Kelvins) is directly proportional to volume
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CHARLES’ LAW
Ex. A balloon with a volume of 1.0L at 25°C is cooled to -190°C. The new volume is…
V1 = V2V1= 1.0L T1 = 25 + 273 = 298KT1 T2 T2 = -190 + 273 = 83K
V2 = 1.0 L x 83 K 298K
V2 = 0.28L = 280mL
V1 = V2
T1 T2
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PRESSURE AND TEMPERATURE: GAY-LUSSACS LAW
Pressure increases proportionally as temperature increases, provided volume and amount remain
constant. Pressure is directly proportional to temperature (in
Kelvins)P T A direct relationship
P = kT
P = k
T
P1 = P2
T1 T2
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EXAMPLEEx. A gas cylinder with a pressure of 1000kPa at
25°C is placed in a boiling water bath. What will the new pressure reading be?
P1 = P2 P1 = 1000kPa T1 = 25 + 273 = 298K
T1 T2 P2 = ? T2 = 100 + 273 = 373K
P2 = 1000kPa x 373 K 298 KP2 = 1252 kPa
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Video!
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PRACTICE!!
Popsicle stick analogy
P. 435 # 2,5 P. 451 # 2-5 Worksheet – “Problems – Gas Laws”