How tightly can I pack wiggling students into a

classroom?

Thermal expansion: Lengths all change by the same factor (percentage)

per degree. TLL o

Why linear in temperature change?

A concrete slab is measured with a steel measuring tape in a room where the temperature is at 20o C and found to measure exactly 10 feet wide. The slab is measured again on a day when the temperature is 27o C. The measurement will be

a) Greater than 10 feetb) Less than 10 feetc) Exactly 10 feet

αsteel=11 x 10-6/oC αconcrete=12 x 10-6/oC

You heat a disc with a hole in it. Will the hole expand or shrink, or stay the

same?

A. ExpandB. ShrinkC. Stay the same

Area Change . . . What will it be proportional to?

TVTVV

TAA

oo

o

3

2

Ideal gases:

Molecules collide like billiard ballsMolecules don’t occupy spaceNever condense into liquids or solids

Don’t existModel a lot of things really well!

Ideal GasesConstant Increase Decreases

N

P

T

V

Ideal GasesConstant Increase Decreases

N

P

T

V

Ideal GasesConstant Increase Decreases

N

P

T

V

Ideal GasesConstant Increase Decreases

N

P

T

V

Ideal GasesConstant Increase Decreases

N

P

T

V

In an ideal gas, if you double the volume of the container, while keeping the temperature and the number of molecules the same, the pressure in

the gas A. DecreasesB. Stays the sameC. Increases

Bk constant NT

PV

R = 8.31 J/moleºK = 0.0831 liter-atm/moleºKn = # of moles

Ideal gas lawkB = 1.38 x 10-23 J/ºK

N is number of atoms or molecules

1 mole =6.02x1023 particles

R constant nT

PV

Watch Units! T must be in Kelvin

2 NEPHI 2:26And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed from the fall they have become free forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the law at the great and last day, according to the commandments which God hath given.

How big is a mole? If the earth was made out of

baseballs .

Pennies to the moon

moles6.8102.5r

r0.74

V

V0.74N

m107.3r

m104.6r

24

3

Baseball

Earth

Baseball

Earth

2 Baseball

6Earth

m108.3d

m1055.1d8

moon

3penny

moles104105.2d

dN 1311

penny

moon

In a liter of water . . .– 55.5 moles

What if I turned that 55 moles of water into steam

at 1 atm?

Suppose we have two jars of gas, one of helium and one of oxygen. If both jars have the same volume, and the two gases are at the same pressure and temperature, which jar contains the greatest number of molecules?A. Jar of helium

B. Jar of oxygenC. Both jars contain the same

number.Consider both gases to obey the ideal gas law. Also note that the mass of an oxygen atom is greater than the mass of a helium atom.

A half-liter spray can is “empty” (you can’t get more out), at 20 C, room

temperature. What is the initial P (in absolute pressure)?

How many molecules are still in the can?

A half-liter spray can is “empty” (you can’t get more out), at 20 C,

room temperature. You throw it into the fire at 600 C. What is

the final P in the can (if it doesn’t burst)

A half-liter spray can is “empty” (you can’t get more out), at 20 C, room temperature. You throw it

into the fire at 600 C.Suppose instead you have .6 moles of water

in the can, which becomes an ideal gas at 600 C. What is the final pressure (in atm) assuming the can does not break.

Exploding balloon

What is the mass of air in this room, assuming it is all O2. Take

V= 1800 m3 and T= 20 C. Moxygen=32 g/mole