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How tightly can I pack wiggling students into a classroom?

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Presentation on theme: "How tightly can I pack wiggling students into a classroom?"— Presentation transcript:

1 How tightly can I pack wiggling students into a classroom?

2 Thermal expansion: Lengths all change by the same factor (percentage) per degree. Why linear in temperature change?

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4 A concrete slab is measured with a steel measuring tape in a room where the temperature is at 20 o C and found to measure exactly 10 feet wide. The slab is measured again on a day when the temperature is 27 o C. The measurement will be a) Greater than 10 feet b) Less than 10 feet c) Exactly 10 feet α steel =11 x / o C α concrete =12 x / o C

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6 You heat a disc with a hole in it. Will the hole expand or shrink, or stay the same? A. Expand B. Shrink C. Stay the same

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

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10 Ideal gases:  Molecules collide like billiard balls  Molecules don’t occupy space  Never condense into liquids or solids  Don’t exist  Model a lot of things really well!

11 Ideal Gases Constant Increase Decreases NPTV

12 Ideal Gases Constant Increase Decreases NPTV

13 Ideal Gases Constant Increase Decreases NPTV

14 Ideal Gases Constant Increase Decreases NPTV

15 Ideal Gases Constant Increase Decreases NPTV

16 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. Decreases B. Stays the same C. Increases

17 R = 8.31 J/moleºK = liter-atm/moleºK n = # of moles Ideal gas law k B = 1.38 x J/ºK N is number of atoms or molecules 1 mole =6.02x10 23 particles Watch Units! T must be in Kelvin

18 2 NEPHI 2:26 And 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.

19 How big is a mole? If the earth was made out of baseballs. If the earth was made out of baseballs. Pennies to the moon Pennies to the moon

20 In a liter of water... In a liter of water... –55.5 moles

21 What if I turned that 55 moles of water into steam at 1 atm?

22 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 oxygen C. 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.

23 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)? What is the initial P (in absolute pressure)? How many molecules are still in the can? How many molecules are still in the can?

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25 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) You throw it into the fire at 600 C. What is the final P in the can (if it doesn’t burst)

26 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 Exploding balloon

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28 What is the mass of air in this room, assuming it is all O 2. Take V= 1800 m 3 and T= 20 C. M oxygen =32 g/mole


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