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Solids

Solids. Definite shape and volume Vibrate around fixed positions Crystalline (ordered arrangement) Salt crystals Shapes shown on periodic table Amorphous (random arrangement) Glass Supercooled liquids  has liquid properties but appear to be solids. Liquids.

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Solids

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  1. Solids • Definite shape and volume • Vibrate around fixed positions • Crystalline (ordered arrangement) • Salt crystals • Shapes shown on periodic table • Amorphous (random arrangement) • Glass • Supercooled liquids  has liquid properties but appear to be solids

  2. Liquids • Definite volume, indefinite shape • More disorganized than solid but still fairly close together • Fluids  flow (both liquids and gases) • Surface tension-attraction between particles on surface • Paperclips float on water • Capillary action-attraction of liquid for a solid • Water in graduated cylinder attracted to glass forms a meniscus

  3. Gases • Assumptions of KMT for gases • 1.large # of tiny particles take up practically no volume • 2. Elastic collisions (no kinetic energy lost) • 3. Continuous, rapid random motion • 4. no forces of attraction • 5. temperature depends on KE KE = ½ mv2 • Gasses likely to follow all assumptions: • Small nonpolar molecules • Normal or low pressure • Normal or high temp

  4. Gases and Pressure • Pressure caused by collisions • Force per area • More collisions =more pressure • Smaller area = more pressure • Measuring pressure • Use barometer • Barometers used to be made of mercury

  5. Force Area Barometer Pressure = Units of Pressure 1 pascal (Pa) = 1 N/m2 1 atm = 760 mm Hg=760 torr = 101,325 Pa =101.325 kPa = 1.013 bar = 14.7 psi or lb/in2 = 29.92 in. Hg

  6. Converting between pressures • If your barometer reads 98 kPa, what is this pressure in atms?

  7. Gases and Pressure • Dalton’s Law of Partial Pressures • Total pressure is sum of partial pressures • PT = P1 + P2 + P3 + ….. (and so on)

  8. Gases and Pressure • Often gases are collected over water. • If we want to know the pressure of the dry gas you need to subtract the water vapor pressure • Appendix A-8 lists water vapor pressure • Pdry gas =Ptotal-PH2O

  9. Gases and Pressure • If you know what percent of the mixture a gas makes up, it will exert that percent of the pressure. • Ex: a mixture of gases is made up of 50% Ar, 20% Xe, and 30% Kr. If the total pressure is 800 torr, what are the partial pressures?

  10. The Gas Laws • Show relationships between • P (pressure) • T (temperature • V (volume) • n (moles of gas)

  11. The Gas Laws • Boyle’s Law • ↑Pressure = ↓volume (inverse relationship) • Other variable must be held constant (n, T) • P1V1 = P2V2 • Example: If the pressure of a 250 mL aluminum can is raised from standard pressure to 4 atms, what will happen to the volume of the can? Temperature and moles are held constant.

  12. Volume Pressure How does Pressure and Volume of gases relate graphically? Temperature, # of particles remain constant

  13. The Gas Laws • Charles’s Law • ↑temperature = ↑volume (directly proportional) • Constants (n, P) • V1 = V2 T1 T2

  14. The Gas Laws • Celcius must be changed to KELVIN • K = 273 + °C • Practice: 13 °C = ____K -10 °C = ____K 200K = ____ °C 0K = ______ °C

  15. The Gas Laws • The temperature of a helium balloon is originally 20oC and has a volume of 600 mL, what will happen to the volume if the temperature drops to 5oC?

  16. Volume Temp How does Temperature and Volume of gases relate graphically? Pressure, particles remain constant

  17. The Gas Laws • Lussac’s Law • ↑temperature = ↑pressure (directly proportional) • Constants (n, V) • P1 = P2 T1 T2

  18. Gas Laws • What must the pressure be in a tire at 300K if the pressure is 20 psi at 275K?

  19. Pressure Temp How does Pressure and Temperature of gases relate graphically? Volume, # of particles remain constant

  20. Summary of the Named Gas-Laws:

  21. The Gas Laws • Combined Gas Law • Puts other laws together • Relationship between P, V, and T • n still must be constant • P1 V1 = P2 V2 T1 T2

  22. Example A toy balloon has an internal pressure of 1.05 atm and a volume of 5.0 L at a temp of 20oC. What will happen to the volume when the pressure is 0.65 atm and temp. is -15oC?

  23. Section 3 – Gas Volumes and the Ideal Gas Law • Avogadro’s Law • Equal volumes of gases at the same temperature and pressure contain equal number of molecules

  24. Section 3 – Gas Volumes and the Ideal Gas Law • Molar Volume of a Gas • 1 mol of gas at STP is 22.4 L (use for . . . . . . . . . Stoichiometry )

  25. Section 3 – Gas Volumes and the Ideal Gas Law • Molar Volume of a Gas • What volume does 0.0685 mol of gas occupy at STP?

  26. Section 3 – Gas Volumes and the Ideal Gas Law • Ideal Gas Law • pV = nRT • R = 0.0821 Latm/molK

  27. Section 3 – Gas Volumes and the Ideal Gas Law • What is the pressure in atm exerted by .5 mol sample of nitrogen gas in a 10.0 L container at 298 K?

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