Upload
kristina-davidson
View
217
Download
2
Embed Size (px)
Citation preview
Ideal Gas Law
AOS 101 Discussion Sections 302 and 303
upload.wikimedia.org
planetoddity.com
www.newmediastudio.org
State Variables State variables are quantities that tell us the
state of a gas Specifically, the atmosphere
Examples of state variables Temperature (T) Pressure (P) Density (ρ) Volume (V) Mass (m) Energy (E)
www.kidsgeo.com
Temperature The temperature of a substance is a
proportional to the average kinetic energy of the molecules in that substance If the temperature increases, the kinetic energy
increases If the temperature decreases, the kinetic energy
decreases T α KEavg
Temperature
T1 > T2
KEavg1 KEavg2
>
>
Assuming that m1 = m2v1 v2>
Temperature in the Atmosphere Troposphere
Temperature decreases with height
~10 km Tropopause
Temperature is constant with height
Stratosphere Temperature increases
with height ~45 km
Stratopause Mesosphere
Temperature decreases with height
~80km Mesopause Thermosphere
Density The density of a substance is defined as the
amount of mass of a substance in a given volume
Density =
ρ =
Density
Which box has the greater density (ρ = m/V)?
= 1 kg
1 m
1 m
1 m
Box 1Mass: 5 kg
Volume: 1 m3
Box 2Mass: 15 kg
Volume: 1 m3
Density: 5 kg/m3
Density: 15 kg/m3
Box 2 is more dense
Density in the Atmosphere Air molecules
decrease in number as you move further away from the Earth’s surface
Density decreases with height
How density changes with altitude (baseball analogy)
Pressure The air pressure is the force per unit area that
the atmosphere exerts on any surface it touches
In this class, we say that the force is the weight on an object
Pressure =
P =
Pressure
Which of these scenarios has the most pressure exerted on the terrain?The mountain has less mass above it than the grassy field,
since the atmosphere is most dense near its surface.
Therefore, using F=mass*gravity and P= force/area, the pressure exerted on the grassy field is greater than that of the pressure exerted on the mountain.
Pressure in the Atmosphere Pressure always,
always, ALWAYS decreases with height
Pressure decreases exponentially with height
Relationship between P, T, and ρ Java applet
chemwiki.ucdavis.edu
Ideal Gas Law
P = ρRTPressure1 mb = 1 hPa = 100 Pa
DensityAir ≈ 1000 kg/m3
Ocean ≈ 1056 kg/m3
Temperature0 °C = 273.15 K
Gas Constant287 J/K·kg
What is an Ideal Gas, anyway? An ideal gas is a gas in which the molecules
move randomly and do not interact with each other
Most gases do behave like an ideal gas Ideal gas law is not suitable for low
temperatures or high pressures Because of phase changes
martine.people.cofc.edu
Holding a Parameter Constant The parameter is unchanging and can be
conceptually ignored Symbolizing the affect of holding a parameter
constant x α y – x is directly proportional to y x α 1/y – x is inversely proportional to y
Examples using P=ρRT Holding density (ρ) constant
P α T Holding pressure (P) constant
T α 1/ρ Holding temperature (T) constant
P α ρ
Constant Pressure (T α 1/ρ)
Think of an infinitely elastic balloon If you heat the balloon, what happens? How does this affect the kinetic energy?
Think of boiling water in a pot What happens to the water as it is heated? What happens when the water reaches the
surface? Java appletblog.gaiam.c
om
whatscookingamerica.net
Constant Temperature (P α ρ)
Think about filling up a tire What are you adding to the
tire? How does this change the
pressure? Think about a leaking balloon
What is the balloon losing? Now, how does this change the
pressure? How do either of these
change the kinetic energy? Remember, temperature is
constantbfgoodrichtires.com
Constant Density (P α T)
Most common parameter to be kept constant Think about the car from the previous
homework Finding the initial footprint
Weight = 1920 lbs and P = 30 psi (lbs/sq in) Use P=Weight/Area to find overall footprint
Going from August to January What happens to the temperature? How does this affect the pressure?
Calculate the final footprint (assuming idealized tires)
Java applet
www.carazed.com
An Air Parcel An invisible, imaginary, and infinitely elastic
container Usually a cubic meter in size (1 m3)
It is used to “test” the atmosphere It does not actually occur in nature Can be used to determine how a portion of the
atmosphere evolves Can be roughly shown with weather balloons Shows atmospheric instability
Extremely useful when studying heat and energy exchange in the atmosphere
voices.washingtonpost.comupload.wikimedia.org www.unca.ed
u