Chapter 13 States of Matter

1. Chapter 13 States of Matter Quiz 13

2. Chapter 13 Objectives • Describe how fluids create pressure and relate Pascal's principle to some everyday occurrences • Apply Archimedes' and Bernoulli's principles • Explain how forces within liquids cause surface tension and capillary action, and relate the kinetic model to evaporation and condensation

3. Chapter 13 Objectives • Compare solids, liquids, gases, and plasmas at a microscopic level, and relate their properties to their structures • Explain why solids expand and contract when the temperature changes • Calculate the expansion of solids and discuss the problems caused by expansion

4. Pressure • Pressure is a result of gas molecules crashing into things. • As the molecules collide with objects (such as walls of a container) they impart a force onto the object. • Momentum is conserved as the objects bounce off and the force is directly related to the time of contact and change in momentum.

5. Pressure: Temperature Influence • Temperature is an indicator of the amount of random kinetic energy or molecules. • As temperature goes up, so does the velocity of the molecules as they crash into the walls. • Temperature up: Increase in pressure

6. Pressure: Volume Influence • Pressure is also related to density (which is a combination of volume and mols). • As density decreases, the molecules are more spread out and have less chance of colliding with the walls, which results in lower pressure. • Density up: Pressure up

7. Pressure • Pressure is measured in many things, but the SI unit is Pascals:Newtons per meters2 • Question: Estimate (to an order of magnitude) the pressure on your feet to the ground.

8. PV = NkT (Don’t Write)) This is the way physicists’ describe gas pressure and volume. • This describes the Microscopic form of gas, where as PV=nRT describes the macroscopic form of gas • N = number of molecules • k = Boltzmann’s constant = 1.38 E-23 J/K • V = Meters Cubed (not Liters) • P = Pascals

9. Other Gas Laws (know these) • The PV = NkT is actually the combined gas law, and often not necessary to use, but always gets the right answer regardless • Charles Law = • Gay-Lussac’s Law = • Boyle’s Law • Avogadro’s =

10. Question • A certain jar is closed. The volume of the jar is 22.4 L and the temperature inside the jar is 273 K. • What happens to the pressure if • Temp is raised? • More gas is added? • Volume decreases?

11. Question • Before going on a trip, you check the tire pressure of your car wheels. The pressure reads 31.0 lb/in2 (214 kPa) at a temperature of 15.0 C. After driving for a few hours, you stop and take the pressure of the tires again. The pressure reads 35.0 lb/in2 (241 kPa). What is the temperature of the air in the tires now (assume no loss of air or change in volume)?

12. Follow up Question • Suppose you then released some air, to keep the pressure between 28-32 psi. If you brought the psi down to 31 again, what will the gauge pressure read when the tires cool back down to 15.0 C?

13. Kinetic Energy and Temperature • Temperature again, is average random kinetic energy. Rolling a ball down a bowling lane does increase the total amount of kinetic energy, but it does not increase the temperature (other than resistance).

14. Kinetic Energy (don’t write equation) • The average kinetic energy of gas molecules is proportional to the absolute temperature of the gas. • Total kinetic energy equals Boltzmann constant times Kelvin

15. Maxwell Boltzmann Graph • A probability graph of what the average kinetic energy of each molecule is. • If all molecules are the same, then the X-axis can become velocity.

17. Maxwell Boltzmann Graph • Some water evaporates before 100 C because temp is an average with a huge range of motion

18. Maxwell Boltzmann Graph • The area under the graph is a fraction of how many molecules are moving this fast at the given temperatures. Low Temperatures have a very high peak, but low average velocity. • High temperatures are much more rounded but extend further on the X-axis.

20. Average* Speed (don’t write eq) • The “average speed” of the gas molecules can be described by the following equation. • m is mass of molecule (kg) • Vrms = not quite the same as average speed. RMS refers to square root of the mean of the speed squared, and is generally higher than average

21. Average speed • What has a larger average speed? Argon (molar mass 40) or Nitrogen (molar mass 28)? • Which molecule would have a larger Maxwell Boltzmann range, Argon or Nitrogen?

22. Archimedes principle • Mass of water displaced equals the buoyant force of the water • If 10 grams of water are displaced by a boat, the boat is lifted with a bouyant force of 10 grams • If your density is less than 1, you can think of the density being a percentage of what is under the water. • Density of 0.9 = 90% of volume under the water • Mercury 13x more dense, 13 times the lift

23. Thermal Expansion of Liquids/Solids • When molecules have more energy, they take up more room. • The range of jiggling is much larger. As temperature goes up, objects increase in size due to the increase in temperature. • Very noticeable for gases, less noticeable for solids and liquids, but still important for some projects.

24. Thermal Expansion • Coefficient of Thermal Expansion • Alpha: A value which states: How much does the material change with temperature? • Change in T is in Kelvin, Change in Length over initial Length

25. Relevance to Engineers • Thermostats have two different metals connected to one another. (Bimetallic) • As temperature changes, one expands faster than the other, causing it to bend (turn on and off switch)

26. Relevance to Engineers • Important for Roads, as joints are left on bridges to expand during warm weather • But not so far apart that when it gets cold they lose contact…

27. Relevance to those scared of the dark… • House creaks during the night as thermal contraction takes place 

28. Relevance to Engineers • St. Louis Arch

29. Some Alpha Values (all E-6) • Brick 1.0 • Glass (Pyrex) 3.25 • Granite 8.0 • Glass (most types) 9.4 • Iron/Steel/Cement 12.0 • Copper 16.0 • Brass 19 • Lead 29

30. Questions • A brass rod of length 10.0cm is at an intial temperature of 20 C. If the temperature increases to 50 C, by what length will the brass rod change? • Two steel rods of length 70.0 m each are separated by 1.0cm at an initial temperature of 273 K. At what temperature do the two steel rods touch?

31. Question • Two steel beams, one of length 10.0 m and the other of length 20.0 m are at the same temperature. Which beam, if either, will have the larger change in length if temperature changes? • Molecularly, what are a few factors which influence the alpha value? How do they affect the expansion?

32. Area and Volume Expansion • If length expands and contracts under temperature changes, then since area and volume are affected by length, they will also expand. • Area Expansion • Volume Expansion

33. Area and Volume Expansion • Liquids and Gases do not have alpha values (for linear expansion) • For Solids, their beta values are 3 times the size of their alpha values (due to 3 dimensional expansion)

34. Questions • A 30cm by 30cm aluminum foil sheet is at an initial temperature of 300 K. What is the new area of the aluminum foil if the temperature decreases by 20 K? • When is the best time to fill up your car with gasoline? Why?

35. Gasoline Question • By what percentage does a change in 20 C (roughly 40 F) make in the volume of 1.0 gallons of fuel? Is filling up in the morning worth it? Beta value of Gasoline = 950 E-6 • (also think about temperature difference below surface of the earth)

36. Question • Water has two beta values: • 0 Degrees C = - 68 • 20 Degrees C = 207 • Explain the difference and what is going on.

37. Capillary Action • The ability of a molecule to pull itself up (through electromagnetic interaction) • Cohesion: Attractive force to oneself • Adhesion: Attractive force to others

38. Solid/Liquid/Gas • Solid Liquid Gas • Strong IMF Middle Weak IMF • Strong Bond Weak Bond No Bond • Fixed position Mobile Position No set • Equal amounts of kinetic energy at same temp • Condensed state of matter Expanded • Little adjustable volume Largely adjustable