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# What changes about the atoms in a substance as it gets warmer? - PowerPoint PPT Presentation

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 ( o C) – based on water. Kelvin (K) – based on absolute Zero. Can it get colder than…

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What changes about the atoms in a substance as it gets warmer?

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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?

273

K = oC +

How can you tell that there is pressure in soda bottle

Before 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.

Lets consider a gas inside a soda bottle.

What could I do to make the pressure inside the soda bottle INCREASE

Gas particles and pressure animation

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 on

anything surrounded by them

Is there any pressure on us now?

Yes, we are in a “Pool of air” at the very bottom

Force

Pressure =

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 pounds

in2

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 thickness of the line

How far out from the earth would 99% of all the atoms in the atomosphere be?

The radius of the earth is 4,000 miles

99% of the atoms in the atmosphere are within 19 miles

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 kg

Or 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

760 mm Hg

How can air pressure pushing down hold up a liquid?

Inventor of the barometer

Evangelista Torricelli

1608-1657

Hired by a pump manufacturer to solve a problem

No matter what was done, water could not be “sucked” up by

a pump more than 32 feet above the water level.

40 ft

new the problem at once.

In attempt to prove his theory he experimented with

mercury filled glass tubes. The height of the mercury column

invariable fell to a height of ________ above the Hg surface

760 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

Height of a column of liquid

or

Area

psi

1 ATM=

14.7

101.35 kPa - kilopascal

mm Hg

760

760 Torr

29.92 in Hg

Standard Temperature & Pressure

STP =

0oC or 273 K

psi

1 ATM=

14.7

101,350 Pa

101.35 kPa - kilopascal

mm Hg

760

760 Torr

29.92 in Hg

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?

Boyle’s Law

P1 V1 = P2 V2

Initial Pressure

Final Pressure

Initial Volume

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

What would the volume of a 6 L balloon be if I doubled its temperature?

(at a constant pressure)

Charles’ Law

V1 V2

=

T1 T2

Final Volume

Initial Volume

Final Temperature (K)

Initial Temperature (K)

V1 & V2 must have the same units

T1 & T2 MUST BE IN KELVIN

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

=

T1 T2

Final Pressure

Initial Pressure

Final Temperature (K)

Initial Temperature (K)

P1 & P2 must have the same units

T1 & T2 MUST BE IN KELVIN

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 weigh

Ideal Gas Laws Assumptions

2.) The particles in a gas are not attracted or repelled from each other.

Generally a good assumption, because the particles are so far apart.

Ideal Gas Laws Assumptions

3.) Collisions of gas particles are totally elastic.

Good!!!!

If the atoms of gas slowed don’t with each collision, what would happen to the gas in this room?

Ideal Gas Laws Assumptions

4.) Temperature measures the average kinetic energy of the particles of a gas.

Good 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 L

What if the temperature was greater than 273 K?

What if the pressure was greater than 1 atm?

PV = nRT

Temperature (K)

Pressure

mole

Volume(L)

Universal Gas Constant

Units must match

kPa L

J

mol K

mol K

So R (universal gas constant) is equal to

R = 8.31

or

R = 8.31

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!

kPa L

J

Mol K

Mol K

PV = nRT

Temperature (K)

Pressure

mole

Volume(L)

Universal Gas Constant

Units must match

R = 8.31

or

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?

J

mol K

R = 8.31

R

k=

NA

Avag

Boltzmann’s constant

(1.38 x 10-23 J/K)

3

2

KE = kT

Temperature (K)

Average kinetic energy of a group of gas particles.

Boltzmann’s constant

(1.38 x 10-23 J/K)

Why is this only the average KE of the atoms?

Don’t write yet

mv2

3

2

= kT

2

rearranging

3kT

Vrms =

m

3kT

In Kelvin

Vrms =

m

Root mean square velocity of an atom in a gas m/s

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???