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UNIT 5: GAS AND ATMOSPHERIC CHEMISTRY11.2 & 11.3 Gas Laws
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
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
ANIMATION
http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/gaslaw/boyles_law_graph.html
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
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
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!
CHARLES’ LAW
Temperature and Volume
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
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
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
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
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
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
Video!
PRACTICE!!
Popsicle stick analogy
P. 435 # 2,5 P. 451 # 2-5 Worksheet – “Problems – Gas Laws”