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Chemistry II

Chemistry II . Unit 1 Gases. The Nature of Gases. Objectives: Describe the assumption of the kinetic theory as it applies to gases. Interpret gas pressure in terms of kinetic theory Define the relationship between Kelvin temperature and average kinetic energy.

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Chemistry II

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  1. Chemistry II Unit 1 Gases

  2. The Nature of Gases Objectives: • Describe the assumption of the kinetic theory as it applies to gases. • Interpret gas pressure in terms of kinetic theory • Define the relationship between Kelvin temperature and average kinetic energy. • Explain why gases are easier to compress than solids or liquids. • Describe the 3 factors that affect gas pressure.

  3. take the shape of their container • low density • Compressible • Mixtures are • homogeneous • Fluids (flow) • Properties of Gases

  4. Gas pressure • Results from collisions of gas particles with an object. • In empty space where there are no particles, there is no pressure and is called a vacuum. • Atmospheric pressure (air pressure): due to atoms and molecules in air. • Barometer: used to measure atmospheric pressure.

  5. Units for measuring pressure: • Pascal (Pa) • Standard atmosphere (atm) • Millimeters of mercury (mmHg) • 1 atm = 760 mmHg = 101.3 kPa • 1kpa = 1000 pa • Standard pressure: 1 atm • Factors affecting gas pressure • Amount of gas • Volume • Temperature • Standard temperature : 0C (273K)

  6. Converting between units of pressure • A pressure gauge records a pressure of 450 kPa. What is the measurement expressed in atmospheres and millimeters of mercury? For converting to atm: 450 kpa x 1 atm = 4.4 atm 1013.kPa For converting to mmHg: 450kPa x 760 mmHg = 3.4 x 103 mmHg 101.3 kPa

  7. What pressure in kilopascals and in atmospheres, does a gas exert at 385 mmHg? 51.3 kPa, 0.507 atm • The pressure on the top of Mount Everest is 33.7 kPa. Is that pressure greater or less than 0.25atm? 33.7 kPa is greater than 0.25 atm

  8. Reaction_to_Air_Pressure_Below_Sea_Level.asf • Classwork: Read pages 103-105 Do problems 1,4,5,6

  9. Gas Laws • Objectives • Describe the relationships among the temperature, pressure, and volume of a gas • Use the gas laws to solve problems

  10. Boyle’s Law : Pressure and Volume • States that for a given mass of gas at constant temperature, the volume of a gas varies inversely with pressure. • If pressure increases, volume decreases; if pressure decreases, volume increases. • Volume could be in liters (L), mL, cm3, dm3 ,m3) 1L=1000 mL 1 cm3= 1 mL

  11. P1 x V1 = P2 x V2 P: pressure 1: initial condition V: volume 2: final condition YouTube - Self Inflating a Balloon Marshmallow Man In A Vacuum (Family & Education: Cool Experiments)

  12. Using Boyle’s Law • A balloon with 30.0L of helium at 103kPa rises to an altitude where the pressure is only 25.0kPa. What is the volume of the helium (at constant temperature)? P1 x V1 = P2 x V2

  13. 2. A gas with a volume of 4.00L at a pressure of 205 kPa is allowed to expand to a volume of 12.0L. What is the pressure of the container now (at constant temperature)? P1 x V1 = P2 x V2

  14. Classwork: pg 121 #1 (a-c), 2, 3, 4

  15. Charles’s Law: Temperature and Volume • States that the temperature of an enclosed gas varies directly with the volume at constant pressure. • As temperature increases, volume increases. V1 = V2 T1 T2 V1: initial volume V2: final volume T1: initial temperature T2: final temperature Temperature has to be in Kelvin scale. K =C + 273

  16. As a gas is heated, it expands. This causes the density of the gas to decrease. YouTube - Balloon in liquid nitrogen Volume and Temperature

  17. Using Charles’s Law • A balloon inflated in a room at 24C has a volume of 4.00L . The balloon is then heated to a temperature of 58C. What is the new volume ? Since temperature increases, you expect the volume to increase. Classwork: p124 # 11, 12 (a-c), 13

  18. Combined Gas Law • Describes the relationship among the pressure, temperature and volume, when the amount of gas is constant. • P1V1 = P2V2 T1 T2 • Standard temperature and pressure (STP): 0C, 1 atm • Useful conversions: 1L =1000 mL ; 1mL =1cm3 ; 1dm3 = 1 L

  19. Using the combined gas law: • The volume of a gas filled balloon is 30.0L at 313K and 153 kPa. What would the volume be at standard temperature and pressure (STP)? Classwork: p 126 #14(a), 15 (a) , 16, 17,

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