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Gases Chem II Chapter 10

Gases Chem II Chapter 10. Characteristics of Gases. 1. Substances that are typically solids or liquids at room temperature are referred to as vapors. ( mercury vapor, water vapor, etc.). Characteristics of Gases. a.Low molar mass b.Expand spontaneously to fill its container

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Gases Chem II Chapter 10

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  1. GasesChem II Chapter 10

  2. Characteristics of Gases

  3. 1. Substances that are typically solids or liquids at room temperature are referred to as vapors. (mercury vapor, water vapor, etc.)

  4. Characteristics of Gases a.Lowmolar mass b.Expandspontaneously to fill its container c. Form homogenous mixtures with each other regardless of the identities or relative proportions of the component gases.

  5. Pressure • Pressure is defined as _________ per unit __________.

  6. Pressure 2.Pressure is defined as force per unit _area. • Formula : P = F/A

  7. Pressure 3.Gas particles exert pressure when they collidewith themselves or with their container.

  8. Pressure 4. B/c the particles in air move in every direction, they exert pressure in alldirections.

  9. Figure 10.01

  10. Pressure 5. This type of pressure is called atmospheric pressure.

  11. Measuring Pressure 6.Italian physicist Evangelista Torricelli (1608 – 1647) was the first to demonstrate that air exerted pressure.

  12. Measuring Pressure 7. The device that Toricelli developed was called the barometer.

  13. Figure 10.02

  14. Measuring Pressure 8. A barometer is an instrument used to measure atmosphericpressure.

  15. Measuring Pressure 9.Gravitypulls down on the column of mercury.

  16. Measuring Pressure 10. A manometeris an instrument used to measure gas pressure in a closed container.

  17. Figure 10.03

  18. Measuring Pressure When the valve between the flask and the u tube is open, gas particles diffuse out of the flask and push the mercury in the tube.

  19. Measuring Pressure 11. The different heightsof the mercury in the two arms is used to calculate the pressure of gas in the flask.

  20. Units of Pressure 12.The SI unit for pressure is the Pascal - one newton of force per one square meter. ( 1N/m2)

  21. Units of Pressure 13. More traditional units include: a.psi- pounds per square inch b.mmHg- millimeters of mercury c. torr= 1 mmHg 1atm = 1 atmosphere = 760 mmHg = 760 torr d.barr- 1 x 105pascal

  22. 1 atm = 760 torr= 760 mmHg=101.3 Kpa=1.013 barr 14. Standard atmospheric pressure ( typical pressure at sea level) is 760 torror 1.01325 x 105 Pa.

  23. Practice conversion • A.) .357 atmospheres to torr • B.) 6.6 x 10-2torr to atmospheres • C.) 147.2 KPa to torr • D.) 745 torr to KPa • E.) .975 atmosphere to Pa and then to KPa

  24. On a certain day the barometer in a laboratory indicates that the atmospheric pressure is764.7 torr. A sample of gas is placed in a vessel attached to an open-end mercury manometer. The level of the mercury in the open end arm of the manometer has a measured height of 136.4 mm and that in the arm that is in contact with the gas a height of 103.8 mm. What is the pressure of the gas in amospheres and in KPa?

  25. The Gas Laws • Boyles Law: • 4 variables define the condition (state ) of a gas. • * Temperature (T) • * Pressure ( P) • * amount of gas ( n) • * volume (V)

  26. The Gas Laws 15. The equations that relate these variables are known as the gas laws: * Boyles * Charles * Gay Lussac * Combined * Ideal

  27. Boyles Law : Pressure - Volume Relationship 16. The volumeof a fixed quantity of gas maintained at constant temperature is inversely proportional to the pressure.

  28. Boyles Law : Pressure - Volume Relationship • The volume of a fixed quantity of gas maintained at constant temperature is inversely proportional to the pressure

  29. Boyles Law : Pressure - Volume Relationship 17. V = constant x 1/P or PV = constant • Boyles Law: P1V1= P2V2

  30. Boyles Law : Pressure - Volume Relationship • Robert Boyles made very careful measurements at constant temperature and proved that increasing the pressure by two reduces the volume by ½ : decreasing the pressure by ½ increases the volume by 2.

  31. Boyles Law : Pressure - Volume Relationship • PV = constant at constant temperature.

  32. Example: A sample of helium gas in a balloon is compressed from 4L to 2.5 L at a constant temperature. If the pressure of the gas in the 4L volume is 210 kPa , what will be the pressure at 2.5L?

  33. Charles LawTemperature and Volume Relationship

  34. Charles LawTemperature and Volume Relationship 18.The French physicist Jacques Charles (1746- 1823) studied the relationship between volume and pressure.

  35. Charles LawTemperature and Volume Relationship 19. When the temperature increases the molecules move fast and hit the walls of the container more often and with more force. If pressure remains constant, the volume must increase.

  36. Charles LawTemperature and Volume Relationship 20.Charles Law states: The volume of a given mass of a gas is directly proportional to its Kelvin temperature at constant pressure. V1= V2 T1T2

  37. Charles LawTemperature and Volume Relationship The temperature must be expressed in __________________ Tk = 273 + Tc

  38. Charles LawTemperature and Volume Relationship 21.The temperature must be expressed in Kelvin. Tk = 273 + Tc

  39. Charles Law exampleA gas sample at 40º C occupies a volume of 2.32 L. If the temperature is raised to 75º C, What will the volume be, assuming pressure is constant?

  40. Gay – Lussac’s Law : Temperature and pressure 22. The pressure of a given mass of gas varies directly with Kelvin temperature.

  41. Gay – Lussac’s Law : Temperature and pressure • When the pressure remains constant… P1 = P2 T1 T2

  42. Example Gay-Lussac problem The pressure of a gas in a tank is 3.2 atm @ 22º C If the temperature raises to 60º C, What will be the gas pressure in the tank?

  43. Combined gas Law : • 23. The Combined gas law statesthe relationship among pressure, volume and temperature of a fixed amount of gas. P1V1 = P2V2 T1 T2

  44. Example Combined Gas Law • A gas at 110 kPa and 30º C fills a flexible container with an initial volume of 2L. If the temperature is raised to 80º C and the pressure increased to 440kPa, what is the new volume?

  45. 24.Avogadro’s Principle : Equal volumes of gas at the same temperature and pressure contain equal numbers of particles.

  46. Avogadro’s Principle : 25.The molarvolumefor a gas is the volume that one mole occupies at 0ºC and 1 atm. of pressure.

  47. Avogadro’s Principle : 26. 1 mole of any gas at standard temperature and pressure (STP) will occupy 22.4 L.

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