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Gases and Liquids

Gases and Liquids. Fluids. Kinetic Molecular Theory. Gases are fluids Gases have low density Gases are highly compressible Gases completely fill a container and exert pressure equally in all direction Gases move faster in higher temperature V=158 √ T MM. Atmosphere is a sea of gases.

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Gases and Liquids

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  1. Gases and Liquids Fluids

  2. Kinetic Molecular Theory • Gases are fluids • Gases have low density • Gases are highly compressible • Gases completely fill a container and exert pressure equally in all direction • Gases move faster in higher temperature • V=158√T MM

  3. Atmosphere is a sea of gases • Atmosphere

  4. The main gases of atmosphere • Percentages:

  5. Atmospheric pressure • Pressure= force on a surface divided by the area of that surface. Its unit in SI Pascal. • Pascal = 1 Newton of force meter squared

  6. Atmospheric pressure (barometer) • 1 atm = 101.3 kpa = 760 torr = 14.7 psi =760 mmHg

  7. Standard temperature and pressure • Standard temperature and pressure STP • STP = 0°C and 1 atm • At sea level the atmospheric pressure is equal to 1 atm. • Atmospheric pressure is lower in a higher altitude and higher in the valley

  8. Pressure conversion • Convert 22 atm into Psi • 22atm X 14.7 psi = 323.4 Psi 1 atm Convert 73 kPa into torr 73 kPa X 760 torr = 547.7 torr 101,3 kPa

  9. Green House effect Earth is becoming warmer

  10. Ozone depletion and free radicals Free radicals such as Chlorine atom

  11. Gas Laws • 1) Boyles law: The volume of a gas at constant temperature is inversely proportional to the pressure. P1V1 =P2V2

  12. Problem • A sample of a gas has a volume of 100 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? P1V1 =P2V2 • 95.9 mL

  13. Dalton’s Law (partial pressure) • The total pressure is equal to the sum of partial pressure. Ptot= P1+ P2 +…

  14. Problem • At a certain temperature, the vapor pressure of water is 20 mmHg. A gas is collected over water at the same temperature at a total pressure of 720 mm Hg . The partial pressure of the gas in mmHg is.. • 700 mmHg or torr

  15. Charles’s Law • The volume of a gas at constant pressure is directly proportional to the absolute temperature.

  16. Charles’s Law • Hot air balloon

  17. Problem • A gas has a volume of 18 centimeter cube at 25 degree Celsius. If the temperature is increased to 35 C at constant pressure, the new volume will be.. • (Hint) T→ Kelvin = 18.6 cm3

  18. Avogadro’s Law • Gases with equal volumes under the same conditions have an equal number of molecules. • I mole of any gas at STP occupies 22.4 liter of volume. • 22.4 liter of any gas at STP has the same number of molecules or atoms

  19. Problem • Calculate the density of oxygen gas at STP. • Density = mass = Molar Mass volume Molar Volume D = 32 = 1.43 g/cm3 22.4

  20. Lussac’s law of combining volume • Gases at constant temperature and pressure form compounds with each other in definite proportions

  21. Lussac’s Law continues

  22. Lussac’s Law continues • In a balanced equation, the coefficients can interpret as volume ratio as well as molecular ratio. • H2 + Cl2 → 2HCl • 1 volume of Hydrogen reacts with one volume of Chlorine to produce 2 volume of HCl

  23. Problem • According to the Lussac’s law during the decomposition of the Ammonia (NH3) to nitrogen gas and Hydrogen gas, what is the volume ratio of the Nitrogen gas to the hydrogen gas in that order? • 1 to 3

  24. Graham’s Law( the law of diffusion) At STP the rate of effusion (diffusion of gasses is inversely proportional to the square root of their molar masses.

  25. Graham’s Law continue • Velocity means rate

  26. What is the rate of effusion of H2 to O2?

  27. Ideal Gas Law • P,V, T and n

  28. Ideal Gas law continues • If the Pressure is kpa R= 8.314 L.kpa mol.K • If the Pressure is atm R= 0.0821 L.atm mol.K

  29. A sample of CO2 with mass of 0.25 g is placed in a 350 mL container at 400 Kelvin. What is the Pressure exerted by the gas? • PV= nRT • n= 0.25 = 0.0057 44 350 mL X 1 liter = 0.35 L 1000mL • P = nRT = (0.0057)( 8.31)(400) V 0.35 • = 54 kpa

  30. Combine law

  31. A sample of oxygen gas has a volume of 7.84 cm3 at a pressure of 71.8 kPa and a temperature of 25 degrees Celsius. What will be the volume of the pressure changes to 101 kPa and the temperature goes down to 0 degrees Celsius? • The formula for combined law is • P1V1 = P2V2 T1 T2

  32. Gas Stoichiometry • How many liters of H2 are needed to react with 22 L of N2 to produce Ammonia? • 3H2+N2→2NH3 • 22 L N2 X 3 L H2= 66 L H2 1 L N2

  33. Forces of attraction • Vapor pressure increases with temperature • H2O (l) ↔ H2O (g) water changes into gas in an open container (evaporation). The opposite of evaporation is condensation. • In a closed container the pressure due to water vapor reaches maximum value which is called vapor pressure.

  34. Phase diagrams

  35. Phase diagrams • Critical point: At 374°C and 22.1 MPa (218 atm) liquid water and vapor have the same density. • Normal boiling point for water is 100°C and 101 kPa. • Triple point of water is the point that three phases of water exist at equilibrium. The triple point of water is 0.01°C and 0.612 kPa. The sublimation region of the graph always lies below the triple point.

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