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Chapter 14 Section 1 & 2. Properties of Gases & The gas Laws. Measurable Properties of Gases. Compressible Have mass Gas particles always in motion Gas particles exert pressure when they run into a wall Take up any shape and size of container – diffuse (= to spread out)
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Chapter 14 Section 1 & 2 Properties of Gases &The gas Laws
Compressible Have mass Gas particles always in motion Gas particles exert pressure when they run into a wall Take up any shape and size of container – diffuse (= to spread out) Are described with four variables: the amount of gas (n), volume (V), pressure (P), and temperature (T) ** variable = something you can change and represented by a letter Properties of Gases
Pressure vs. Volume(Boyle’s Law) Describe the picture.
Boyle’s Law Equations • P1∙V1 = P2∙V2 • “1” and “2” refer to two different sets of condition • Match the unit for each variable • The volume is inversely proportionalto the pressure • The volume increases (decreases) as the pressure decreases (increases) • The temperature and amount of gas must remain unchanged for this law to work
Example A given sample of gas occupies 523 mL at 760 torr. The pressure is increased to 1.97 atm, while the temperature remains the same. What is the new volume of the gas?
Practices on Boyle’s Law 1) A flask containing 155 cm3 of hydrogen gas was collected under a pressure of 22.5 kPa. What pressure would have been required for the volume of the gas to have been 90.0 cm3?
2) 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 the constant?
3) A gas has a pressure of 1.26 atm and occupies a volume of 7.40 L. If the gas is compressed to a volume 2.93 L, what will its pressure be, assuming constant temperature?
Charles’S Law 1) 2) The volume and temperature are directly proportional 3) The volume of gas increases (decreases) as the temperature increases (decreases) 4) The temperature MUST be in kelvin (K = C + 273) 5) Must keep the pressure and the amount of gas unchanged for this law to work
Example A balloon is inflated to 665 mL volume at 27°C. It is immersed in a dry-ice bath. What, at −78.5°C, is its volume, assuming the pressure remains constant?
Practices 1) A sample of neon gas occupies a volume of 752 mL at 25 ºC. What volume will the gas occupy at 50 ºC if the pressure remains constant?
2) A helium-filled balloon has a volume of 2.75 L at 20 ºC. The volume of the balloon decreases to 2.46 L after it is placed outside on a cold day. What is the outside temperature?
3) A gas at 65 ºC occupies 4.22 L. At what Celsius temperature will the volume be 3.87 L, assuming the same pressure?
Combined Gas Law(Volume, Temperature & Pressure) • Combine Boyle’s law and Charles’s law: • For this law to work, the amount of gas must remain unchanged • With this law, 2 variables out of 3 can change
Example 520 mL of hydrogen gas at 750 mmHg and 25 °C is placed in a 1000. mL container and heated to 50 °C. What is the pressure of the gas in the container?
Boyle’s law: at constant temperature Charles’ law: at constant pressure Gay-Lussac’s law: at constant volume From Combined gas law to….
Gay-Lussac’s Law(Temperature-Pressure Relationship) • Temperature and pressure are directly proportional: • Temperature MUST be in kelvins • Works only if the volume and the amount of gas are kept constant
Example An aerosol can containing gas at 101 kPa and 22 ºC is heated to 55ºC. Calculate the pressure in the heated can. Answer: P2=112kPa
Avogadro’s Law • The volume (V) of gas is directly proportional to the number of moles (n) of gas: • The type of gas doesn’t affect the volume; only the # of moles of gas does • 1 mol of ANY gas at 1 atm and 0˚C takes up 22.4 L volume. • For this law to work, pressure and temperature must remain unchanged
P1∙V1 = P2∙V2 Combine Boyle, charles, & Avogadro’s law
1 mol of ANY gas at 1 atm and 0˚C takes up 22.4 L volume Combine the two above information and get… Ideal Gas Law
Determine the Celsius temperature of 2.49 moles of gas contained in a 1.00-L vessel at a pressure of 143 kPa. Example
Combine V, P, n, and T into one law. From the combined gas law, get Boyle’s law Charles’ law Gay-Lussac’s law Avogadro’s law Ideal gas law Summary of gas laws
Kinetic Molecular Theory 1) Gas particles are in constant, rapid, and random motion 2) The distance between gas particles are much larger than the size of atoms *The size of gas particle is almost nothing. 3) Gas particles colliding with surface creates pressure 4) Perfect elastic collisions between gas particles – no loss of energy during collisions but all transferred 5) Average kinetic energy of gas particles is proportional to kelvintemperature 6) Gas particles at the same temperature don’t have the same amount of kinetic energy (See the graph on the next slide)
Gas particles attract or repel each other Gas particles do have a volume Imperfect collision – energy lost Non-ideal behavior becomes more ideal at high temperature and low pressure Non-Ideal gas behavior
