How tightly can I pack wiggling students into a classroom?

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?

4. 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 bea) Greater than 10 feetb) Less than 10 feetc) Exactly 10 feet αsteel=11 x 10-6/oCαconcrete=12 x 10-6/oC

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

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

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 N P T V

12. Ideal Gases Constant Increase Decreases N P T V

13. Ideal Gases Constant Increase Decreases N P T V

14. Ideal Gases Constant Increase Decreases N P T V

15. Ideal Gases Constant Increase Decreases N P T V

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 • Decreases • Stays the same • Increases

17. Ideal gas law kB = 1.38 x 10-23 J/ºK N is number of atoms or molecules R = 8.31 J/moleºK = 0.0831 liter-atm/moleºK n = # of moles 1 mole =6.02x1023 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 . • Pennies to the moon

20. 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? • Jar of helium • Jar of oxygen • 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)? • How many molecules are still in the can?

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)

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

28. 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