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States of Matter: Gases

States of Matter: Gases. Unit Objectives. Describe the properties of gases. Describe how pressure is measured Convert between various units of pressure Explain the relationships among pressure, volume, temperature, and amount of gas

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States of Matter: Gases

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  1. States of Matter: Gases

  2. Unit Objectives • Describe the properties of gases. • Describe how pressure is measured • Convert between various units of pressure • Explain the relationships among pressure, volume, temperature, and amount of gas • Use Boyle’s Law, Charles’s Law, Avogadro’s Law, Combined Gas, and Ideal Gas Laws to calculate changes in pressure, volume, temp. and amount of gas.

  3. Unit Objectives • Solve Problems using Dalton’s Law of partial pressures • Describe the assumptions on which the kinetic molecular theory is based • Calculate root mean square speeds of molecular gases • List two molecular properties responsible for deviation from ideal gas behavior. • Identify the conditions under which gases will be most likely to behave in a non-ideal manner • Explain, compare and contrast diffusion and effusion of gases • Calculate the pressure of a real gas as predicted by the van der Waals equation. • Perform calculations for gases collected over water

  4. Gaseous State of Matter • has no distinct shape or volume so fills any container • is easily compressed • mixes completely with any other gas • exerts pressure on its surroundings

  5. Measuring Pressure • barometer: • measures atmospheric pressure • invented by Torricelli, Italian scientist in 1643 • glass tube filled with mercury is inverted in a dish • mercury flows out of the tube until pressure of the Hg inside the tube is equal to the atmospheric pressure on the Hg in the dish

  6. Measuring Pressure • atmospheric pressure: • results from mass of air being pulled toward the earth by gravity • varies with altitude and weather conditions

  7. Measuring Pressure • manometer: • measures pressure of gas in a container • gas has less pressure than atmosphere if the Hg is closer to chamber • gas has more pressure than atmosphere if the Hg is further from chamber • gas pressure = atmospheric pressure ± h

  8. Units of Pressure • mmHg: most common since use Hg in manometers and barometers • torr: equal to mmHg • standard atmosphere (atm) • Pascal (Pa): SI unit; equal to N/m2 1atm = 760mmHg = 760torr = 101,325Pa = 101.325kPa Example

  9. States of Matter: Gases Part 2 Gas Laws

  10. Boyle’s Law • Discovered by Irish chemist, Robert Boyle • Used a J-shaped tube to experiment with varying pressures in multistory home and effects on volume of enclosed gas • P and V are inversely proportional • PV = k • holds precisely at very low pressures Example

  11. Charles’ Law • discovered by French physicist, Jacques Charles in 1787 • first person to fill balloon with hydrogen gas and make solo balloon flight • V and T are directly proportional • V = kT

  12. Charles’ Law • for any gas, at -273.2°C, the volume is zero • since negative volumes cannot exist, there cannot be a temperature lower than absolute zero (-273.2°C or 0 K) • never actually been reached (0.000001 K has been) • Kelvin system has no negative values Example

  13. Avogadro’s Law • Discovered by Italian chemistry, Avogadro in 1811 • proposed that equal volumes of gases at the same temperature and pressure contain the same number of particles • V = kn • V and n are directly proportional Example

  14. Gay-Lussac’s Law • discovered in 1802 by Joseph Gay-Lussac • P = kT • P and T are directly proportional Example

  15. Example: Pressure Conversions The pressure of a gas is measured as 49 torr. Represent this pressure in atmospheres, Pascals, and mmHg.

  16. Example: Boyle’s Law Consider a 1.53-L sample of gaseous SO2 at a pressure of 5.6 x 103 Pa. If the pressure is changed to 1.5 x 104 Pa at constant temperature, what will be the new volume of the gas?

  17. Example: Charles’ Law & Temp. A sample of gas at 15°C and 1 atm has a volume of 2.58 L. What volume will this gas occupy at 38°C and 1 atm?

  18. Example: Avogadro’s Law Suppose we have a 12.2-L sample of gas containing 0.50 mol O2 at a pressure of 1 atm and temperature of 25°C. If all of this O2 were converted to O3 (ozone) at the same temperature and pressure, what would be the volume of O3?

  19. Example: Gay-Lussac’s Law 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 temperature exceeds 52°C. What would the gas pressure be in the can at 52°C?

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