What changes about the atoms in a substance as it gets warmer? They move faster! ltzmann distribution applet
Jan 22, 2016
What changes about the atoms in a substance as it gets warmer?
They move faster!
boltzmann distribution applet
What are 3 Temperature Scales that we use?
Fahrenheit – Not used in Science
Celsius (oC) – based on water
Kelvin (K) – based on absolute Zero
Can it get colder than…
0oF
0oC
0 K
ABSOLUTE ZERO- atoms slow down as a sample gets colder.
What is the slowest that atoms can move?
K = oC + 273
How can you tell that there is pressure in soda bottleBefore you open it?
If you push on it, it pushes back right?
The pressure on the inside of the bottle, has two components:
Area
Force
The area is easy– the inside of the bottle
BUT WHAT IS CAUSING THE FORCE?????
How can molecules of air exert a force on the inside of the container?
Do they push?
What are the air molecules in the room doing now?
Moving, but how?
In a straight line until….
If the pressure is cause by collisions (like cars) why don’t I see things getting bounced around?
But molecules are so small and light.
How can they produce enough force that I can feel it push back against a soda bottle.
Gas particles and pressure animation
Lets consider a gas inside a soda bottle.
What could I do to make the pressure inside the soda bottle INCREASE
Add more gas because….
3 ways to increase pressure of a gas inside a container:
Increase the temperature because….
Decrease the volume of the container because…
Can only liquid be fluids?
Both liquids and gases are fluids and exert a pressure onanything surrounded by them
Is there any pressure on us now?
Yes, we are in a “Pool of air” at the very bottom
Pressure =Force
Area
What is the force on 1 in2 due to air.Guess by the weight of so many paperclips
Demo: Magdeburg sphere
Why were the spheres so hard to open after using the vacuum pump?
Why were the spheres so EZ to open after the valve was opened?
Other than opening the valve to let air in, what else would make the spheres easy to open?
If we could get a perfect vacuum inside the sphere, would it be possible to open them?
The equivalent of a stack of paperclips would be
6700 on every square inch of your body
Air pressure is pushing down
14.7 poundsin2
The spheres have an area of about 11 in2 on each side = 160 # pulling on each side
Gases fill a container right?
What is the container on the earth?
Why doesn’t the gas leave to fill the universe?
The top of a sea of water is very easy to see right?What about the top of the atmosphere?
The radius of the earth is 4,000 miles
99% of the atoms in the atmosphere are within 19 miles
The thickness of the line
How far out from the earth would 99% of all the atoms in the atomosphere be?
How much would the air in this room weigh?
The volume of the room is about
10*30*20 = 6000 m3
The density of air (at ground level) is 1.25 kg/m3
The mass of the air in this room is about 7500 kgOr 3,300# ( the weight of a car!!!!!)
If I fill a test tube full of water and invert it in a cup of water what happens?
Could I do this with a 1 foot test tube of water?
Could I do this with a 10 foot test tube?
Could I do this with a 100 foot test tube?
There is a limit to the height of a water column that air pressure will hold up!
WHY?
Average air pressure will push up ~32 ft of water.
Why did I say average?
What happens to the water column when air pressure goes up?
A 32 foot barometer is not too practical, how could I make it shorter?
No pressure
Atmospheric Pressure
How can air pressure pushing down hold up a liquid?
760 mm Hg
Evangelista Torricelli
1608-1657
Inventor of the barometer
Hired by a pump manufacturer to solve a problem
No matter what was done, water could not be “sucked” up bya pump more than 32 feet above the water level.
40 ft
He had read Galileo’s work on the weight of air, and new the problem at once.
In attempt to prove his theory he experimented withmercury filled glass tubes. The height of the mercury columninvariable fell to a height of ________ above the Hg surface760 mm
The prominent scientific theory as to what held the column up was that “nature abhors a vacuum”
He reasoned that if the resistance to vacuum has holding up the column. Then a taller tube should have a taller column of mercury
But……..
Another theory was that invisible strings were holding the liquid up
But the his theory was generally accepted after he took his barometer climbing
The level dropped the higher he climbed!!
Pressure can be expressed two ways
Force
Areaor Height of a column of liquid
1 ATM = 14.7101.35 kPa - kilopascal
760 mm Hg760 Torr
29.92 in Hg
psi
STP =0oC or 273 K
Standard Temperature & Pressure
1 ATM = 14.7
101.35 kPa - kilopascal760 mm Hg760 Torr
29.92 in Hg
psi101,350 Pa
How does a drinking straw work?
You suck up the liquid right?
How strong is a balloon?
If there is 14.7 POUNDs crushing down on every square inch of the outside of a fragile balloon,
WHY IS IT NOT CRUSHED????
What would happen if I increased the pressure on the outside of the balloon by taking it under water?
It decreases in volume, WHY?
As the volume decreases, the pressure goes up Right?
Because the air molecules repel each other?
For a gas
Pressure Volume
What would the volume of a 6 L balloon be if I doubled the pressure on it?
P1 V1 = P2 V2
Boyle’s Law
Initial Pressure
Initial Volume
Final Pressure
Final Volume
P1 & P2 CAN HAVE ANY UNITS but they must match
V1 & V2 CAN HAVE ANY UNITS but they must match
What would happen if I took a balloon and put it in the fridge?
Why?
What is the same B4 & After?
For a gas
Temperature Volume
(at a constant pressure)
What would the volume of a 6 L balloon be if I doubled its temperature?
V1 V2
Charles’ Law
Initial Temperature (K)
Initial Volume
Final Temperature (K)
Final Volume
T1 & T2 MUST BE IN KELVIN
V1 & V2 must have the same units
T1 T2
=
Taking a balloon out for a stroll
What if an aerosol can was placed in a fire, assuming it does not rupture what changes?
For a gas
Temperature Pressure
Assuming that ….
P1 P2
Initial Temperature (K)
Initial Pressure
Final Temperature (K)
Final Pressure
T1 & T2 MUST BE IN KELVIN
P1 & P2 must have the same units
T1 T2
=
Practice
What is the volume of a 10 L balloon if the pressure on it is increased from 2 atm to 6 atm?
What would the pressure of a rigid can at 50 Pa if its temperature was raised from 150 K
to 300 K?
150 oC to 300 oC?
In order to make a 5 gallon balloon at 100 Kelvin shrink to 1 gallon, what would the
final temperature be?
What would the volume of a 6 L balloon be if I doubled its temperature and pressure?
Ideal Gas Laws Assumptions
1.) The particles in a gas make up a negligible amount of volume of the gas itself.
Is this an ok approximation, if so when?
Ideal Gas Laws Assumptions
1.) The particles in a gas make up a negligible (unimportant) amount of volume of the gas itself.
Good most of the time – atoms in a gas take up less than 1/1000th of the volume of a gas.
What is between the atoms?
A neutron star is nearly solid matter, a teaspoon of it would weighabout 10,000,000 tons
Ideal Gas Laws Assumptions
Generally a good assumption, because the particles are so far apart.
2.) The particles in a gas are not attracted or repelled from each other.
good or bad assumption?
Ideal Gas Laws Assumptions
Good!!!!
3.) Collisions of gas particles are totally elastic.Demo- happy / sad balls
If the atoms of gas slowed don’t with each collision, what would happen to the gas in this room?
good or bad assumption?
Ideal Gas Laws Assumptions
Good assumption
4.) Temperature measures the average kinetic energy of the particles of a gas.
good or bad assumption?
As the temperature of a gas goes up its particles move faster!
What did we use in chemistry to talk about the number of atoms in a
sample?
THE MOLE
1 mole of something = 6.022 x 1023 pieces of something
NA
1 MOLE of ANY gas
at STP has a volume of
22.4 LWhat if the temperature was greater than 273 K?
What if the pressure was greater than 1 atm?
PV = nRT
Pressure
Volume(L)
mole
Universal Gas Constant
Temperature (K)
Units must match
R = 8.31
Jmol K
So R (universal gas constant) is equal to
kPa Lmol K
R = 8.31
or
This is the standard PHYSICS R to use, there are others based on different unit of pressure.
At STP, 1 mole of a gas occupies 22.4 L
NO MATTER WHAT THE GAS IS!!!
At STP, 1 mole of He has a volume of 22.4 L
At STP, 1 mole of CO2 has a volume of 22.4 L
What is different?SF6 boat demo
How is it that even though a CO2 molecule is bigger than a H2
molecules, the gases occupy the same VOLUME?
The particles are so far apart, most of the volume of a gas is
NOTHING!
PV = nRT
Pressure
Volume(L)
mole
Universal Gas Constant
Temperature (K)
Units must matchR = 8.31 kPa L
Mol KJ
Mol Kor
How much space would 3.5 mol of N2 require at 305 K and 250 torr?
If .52 mole of Ar is trapped in a 50 mL syringe at 25oC, what is the pressure
inside the syringe?
At what temperature would 8.5 x 1024 molecules of CO2 exert a pressure of
193 kPa in a 25.3 L tank?
What is the density of N2 gas at 1 atm and 350oC?
Rk = NABoltzmann’s constant
(1.38 x 10-23 J/K)
Jmol KR = 8.31
Avag
KE = kT32
Average kinetic energy of a group of gas
particles.
Boltzmann’s constant(1.38 x 10-23 J/K)
Temperature (K)
Why is this only the average KE of the atoms?
3kT
32
mv2
2rearranging
Vrms =
= kT
m
Don’t write yet
3kTVrms = mRoot mean
square velocity of an atom in a
gas m/s
In Kelvin
Mass of atom or molecule in kg
1 amu = 1.6605x10-27 kg
What is the average speed of a nitrogen molecule in this room at a temperature of 25oC lets find out?
Guesses first???