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Solids, Liquids, & Gases Chapter 7

Solids, Liquids, & Gases Chapter 7. The Nature of Gases. Indefinite shape and indefinite volume expand to fill their containers compressible Fluid – they flow Low density 1/1000 the density of the equivalent liquid or solid Undergo effusion and diffusion. Diffusion.

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Solids, Liquids, & Gases Chapter 7

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  1. Solids, Liquids, & GasesChapter 7

  2. The Nature of Gases Indefinite shape and indefinite volume expand to fill their containers compressible Fluid – they flow Low density 1/1000 the density of the equivalent liquid or solid Undergo effusion and diffusion

  3. Diffusion • Diffusion: describes the mixing of gases. The rate of diffusion is the rate of gas mixing.

  4. Effusion • Effusion: describes the passage of gas into an evacuated chamber

  5. Pressure • Is caused by the collisions of molecules with the walls of a container • Is equal to force/unit area • P=F/A • SI units = Newton/meter2 = 1 Pascal (Pa) • 101,325 Pa = 1 standard atmosphere (1atm) • 1 atm = 760mmHg = 760 torr

  6. Measuring Pressure • The first device for measuring atmospheric pressure was developed by Evangelista Torricelli during the 17th century. • The device was called a “barometer” • Baro = weight • Meter = measure

  7. An Early Barometer • The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.

  8. The Aneroid Barometer

  9. The Digital Barometer

  10. GAS LAWS Boyle’s Law Charles’ Law Gay-Lussac’s Law

  11. BOYLE’S LAW The Relationship Between Pressure and Volume

  12. Robert Boyle(1627-1691) • Boyle was born into an aristocratic Irish family • Became interested in medicine and the new science of Galileo and studied chemistry.  • A founder and an influential fellow of the Royal Society of London • Wrote prolifically on science, philosophy, and theology.

  13. Boyle’s Law • Boyle’s Law: The volume of a gas is inversely proportional to the pressure applied to the gas when the temperature is kept constant. • Decrease in volume = Increase in pressure. • Increase in volume = Decrease the pressure

  14. Boyle’s Equation: • P1V1 = P2V2 • Therefore: • V1=(P2V2)/P1 • V2= (P1V1)/P2 • P1=(P2V2)/V1 • P2=(P1V1)/V2

  15. Problems • You have a 2L cylinder of gas that is under 100 kPa of pressure. If you compress the gas to 1L, what will the new pressure be? • You have a 10.0L container of gas under 505 torr of pressure. If you increase the pressure to 1155 torr, what will the new volume be?

  16. The Relationship Between Temperature and Volume

  17. Jaques Charles (1746-1823) • Charles studied the compressibility of gases nearly a century after Boyle • French Physicist • Conducted the first scientific balloon flight in 1783

  18. Charles’ Law • At a fixed pressure, the volume of a gas is proportional to the temperature of the gas. • As the temperature increases, the volume increases. • As the temperature decreases, the volume decreases.

  19. How Did He Figure It Out? • Acylinder with a piston and a gas is immersed in a water bath. • A mass is placed on top of the piston which results in a pressure on the gas. This mass is held constant, which means that the pressure on the gas is constant. • The gas volume is measured as the temperature is increased and V vs. T data point plotted. This is continued over a large range of temperatures.

  20. Charles’ Equation • Rearrange the equation to solve for V1, T1, V2, or T2 • V1=(V2T1)/T2 • T1=(V1T2)/V2 • V2=(V1T2)/T1 • T2=(V2T1)/V1 • All temperatures must be in KELVIN!!!

  21. Problems • A cylinder contains 5.00L of gas at 225K. If the temperature is increased to 345K, what will the new volume be? • A tire contains 2.00L of air at 300.0K, if the volume in the tire decreased to 1.50L, what must the new temperature be? • A ball contains 3.0L of air at 32ºF, if the volume increases to 5L, what must the temperature have changed to?

  22. Gay-Lussac’s Law The Relationship Between Pressure and Temperature

  23. Joseph Louis Gay-Lussac1778 - 1850 • French chemist and physicist • Known for his studies on the physical properties of gases. • In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes

  24. Gay-Lussac’s Law • The pressure of a fixed amount of gas at fixed volume is directly proportional to its temperature in Kelvin. • As the temperature increases, the pressure also increases • As the temperature decreases, the pressure also decreases

  25. Gay-Lussac’s Law • Expressed Mathematically as: • Rearranging this equation to solve for the variables gives us: • P1=(P2T1)/T2 • P2=(P1T2)/T1 • T1=(P1T2)/P2 • T2=(P2T1)/P1

  26. Problems • Jim-Bob has revved his engine enough so that the internal temperature and pressure of his engine are 700.0K and 200.0kPa. If the temperature outside was 295K before Jim-Bob got into his car, what was the internal pressure in his engine? • Today, the barometer reads 750mmHg and the thermometer says that it is 65ºF. At 6am, the barometer read 700mmHg, what was the temperature at that time?

  27. The Combined Gas Law The Relationship Between Pressure, Volume, and Temperature

  28. The Combined Gas Law • A combination of Boyle’s, Charles’, and Gay-Lussac’s laws. • Written mathematically as: • Temperature must be in KELVIN.

  29. Rearranged to solve for each variable: • P1=(P2V2T1)/(V1T2) • V1=(P2V2T1)/(P1T2) • T1=(P1V1T2)/(P2V2) • P2=(P1V1T2)/(V2T1) • V2=(P1V1T2)/(P2T1) • T2=(P2V2T1)/(P1V1)

  30. Problems • Rhonda’s helium balloon has a volume of 2.00L at 2.00atm and 395K. If the temperature is raised to 500.K and the gas is compressed to 1.00L, what is the new pressure? • Ryan ate at Taco Smell last night. He now has gas which takes up 1.29L of bowel space under 2.35atm of pressure at 310K (body temp). What will be the volume of Jeremy’s gas after he expels it if the atmospheric temperature and pressure are 75ºF and 1.00atm respectively?

  31. Avogadro’s LawThe Relationship Between Pressure, Temperature, Volume and Moles

  32. Amedeo Avogadro(1776-1856) • Italian physicist and mathematician • Born in a noble ancient family of Piedmont • “Avogadro’s Number” is named after him • 6.022 x 1023 • The number of things in a mole

  33. Avogadro’s Law • One mole of any gas occupies exactly 22.4 liters (dm3) at STP. • STP = Standard Temperature and Pressure • Temp = 0ºC = 273K • Pressure = 1atm = 760 mmHg = 760 torr etc. • This is often referred to as the “molar volume” of a gas.

  34. Equal volumes of gases, at the same temperature and pressure, contain the same number of particles, or molecules. • Thus, the number of molecules in a specific volume of gas is independent of the size or mass of the gas molecules. • Therefore, IT DOESN’T MATTER WHICH GAS YOU ARE TALKING ABOUT.

  35. Problems • Luis has 3.5 mol of H2 gas at STP. What volume will this gas occupy? • Joann has a can of CO2 gas that contains 0.180 mol CO2 at 1atm and 273K. If Joann let half of the gas out, what would the new volume be?

  36. Avogadro’s Law • Written mathematically: • Where “n” is the number of moles of gas present • Mini Version:

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