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Physical Characteristics of Gases

Physical Characteristics of Gases. Chapter 14. The Kinetic Molecular Theory. The theory that explains the behavior of gases at the molecular level. The Kinetic Molecular Theory. Gases consist of large numbers of tiny particles that are far apart relative to their size

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Physical Characteristics of Gases

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  1. Physical Characteristics of Gases Chapter 14

  2. The Kinetic Molecular Theory • The theory that explains the behavior of gases at the molecular level.

  3. The Kinetic Molecular Theory • Gases consist of large numbers of tiny particles that are far apart relative to their size • Collisions between gas particles and between particles and container walls are elastic collisions. • Gas Particles are in continuous, rapid, random motion. They posses kinetic energy

  4. The Kinetic Molecular Theory continued 4) There are no forces of attraction or repulsion between gas particles 5) The average kinetic energy of gas particles depends on the temperature of the gas

  5. Expansion • Gases do not have a definite shape or volume • They fill the container that they are in

  6. Fluidity • Gas particles glide easily past one another • This ability to flow causes gases to behave similarly to liquids • Gases are also referred to as fluids

  7. Low Density • Gases are mostly empty space • Compared with liquids and solids, gases have a very low density.

  8. Compressibility • Gas particles, which are initially far apart, are crowded closer together • The volume of a given sample of a gas can be greatly decreased

  9. Diffusion and Effusion • Gases spread out and mix with one another, even without being stirred. • Such spontaneous mixing of the particles of two substances caused by their random motion is called diffusion • Ex. Perfume, air freshener

  10. Effusion • Effusion is the process by which gas particles pass through a tiny opening. • Molecules of low mass effuse faster than molecules of high mass

  11. Graham’s Law of Effusion

  12. The Gas Laws

  13. Pressure and Force • Pressure (P) is defined as the force per unit area on a surface • The SI unit for pressure is the newton, N • A newton is the force that will increase the speed of one kilogram mass by one meter per second each second it is applied

  14. Units of Pressure • Millimeters of mercury (mmHg) • Torr • Atmosphere of pressure (atm) • Pascal (Pa) 1 Pa = 1 N/m2 * Pascal is a small unit,(1000 Pa= 1 kilopascals (kPa) 760 mmHg = 760 torrs = 101.3 kPa = 1 atm

  15. Standard Temperature and Pressure • Abbreviated STP • Standard temperature is 0°C • Standard Pressure is 1 atm • What is the standard pressure in torrs? 760 torrs in mmHg? 760 mmHg In kPa? 101.3 kPa

  16. Boyle’s Law: Pressure-Volume Relationship • Robert Boyle • Series of experiments supported the idea that pressure (P) and volume (V) were inversely proportional • Also, found that with a given gas, the relationship between P and V equaled a constant, k

  17. Boyle’s Law • Can be used to compare changing conditions for a gas P1V1 = k P2V2 = k Two quantities that are equal to the same thing are equal to each other P1V1 = P2V2

  18. Question • A sample of oxygen gas has a volume of 150 mL when its pressure is 0.947 atm. What will the volume of the gas be at a pressure of 0.987 atm if the temperature remains constant?

  19. Charles Law: Volume Temperature Relationship • Quantitative relationship between volume and temperature • Discovered by French scientist, Jacques Charles in 1787 • Found that raising the temp to 1°C causes the gas volume to increase by 1/273 of the volume it had at 0°C

  20. Cooling a gas • The same regularity of volume change occurs if a gas is cooled at constant pressure

  21. Absolute zero • Absolute zero is a theoretical point at which all movement stops • Absolute zero is -273.15 °C or 1 Kelvin (K)

  22. Kelvin Temperature • Fahrenheit scale • Celsius scale • Kelvin scale is a scale that starts at a temperature of -273.15 °C • Absolute Zero is the value of zero in the Kelvin scale K = 273.15 + °C

  23. Charles’ Law • Relationship between Kelvin temperature and gas volume • States that the volume of a fixed mass of gas at constant pressure varies directly with the Kelvin temperature V = kT or V = k T At constant pressure T is the temperature in Kelvins

  24. Charles’ Law V1 = V2 T1 T2

  25. Question #3 • A sample of neon gas occupies a volume of 752 mL at 25°C. What volume will the gas occupy at 50°C if the pressure remains constant?

  26. Gay-Lussac’s Law • The pressure of a fixed mass of gas at constant volume varies directly with the Kelvin temperature. P = kT or P = k T

  27. Gay Lussac’s Law P1 = P2 T1 T2

  28. Question #4 • The gas in an aerosol can is at a pressure of 3.00 atm at 25 °C. Directions on the can warn the user not to keep the can in a place where the temperature exceeds 52 °C. What would the gas pressure in the can be at 52 °C?

  29. The Combined Gas Law • The combined gas las expresses the relationship between pressure, volume and temperature of a fixed amount of gas. PV = k T

  30. Combined Gas Law P1 V1 = P2 V2 T1 T2

  31. Question #5 • A helium filled balloon has a volume of 50.0 L at 25°C and 1.08 atm. What volume will it have at 0.855 atm and 10°C?

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