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The Behavior of Gases

The Behavior of Gases. How do we describe this stuff?. The concept of an IDEAL (perfect) GAS is a model that is used to explain the behavior of gases . The Kinetic Molecular Theory explains the behavior of an ideal gas as it relates the individual particles that make up the gas. .

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The Behavior of Gases

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  1. The Behavior of Gases

  2. How do we describe this stuff? The concept of an IDEAL (perfect) GAS is a model that is used to explain the behavior of gases. The Kinetic Molecular Theory explains the behavior of an ideal gas as it relates the individual particles that make up the gas.

  3. The Kinetic Molecular Theory It states that the gaseous particles: • are in constant random motion • are separated by great distances relative to their size; the volume of the gas particles is considered negligible (insignificant) • have no attractive forces between them • have collisions that may result in the transfer of energy between gas particles, but the total energy of the system remains constant

  4. Real vs Ideal gases • REAL gases do not behave like ideal gases. Their particles do have volume, and they do have forces of attraction (IMF) between their particles. • The farther apart the molecules of a real gas, the more they will act like ideal gases • Light gases at high temperatures and low pressures behave most like ideal gases (this is when they are spread out the most). • EX) H2(g) and He(g)

  5. The space occupied (volume) by a gas is effected by pressure, temperature, and the number of gasesous particles (moles).

  6. Boyle’s Law • describes the effect that changing the pressure on a gas has on its volume • Recall that pressure is the force that is exerted on a given area • The volume of a given mass of gas is inversely proportional to the pressure exerted on it, at constant temperature.

  7. Boyle’s Law • When the volume of a sample of gas is multiplied by its pressure, the value is a constant V x P = k • Therefore, we use the following relationship to work through these problems: P1V1 = P2V2

  8. What volume will 50.0 mL of a gas at 50.6 kPa occupy if the pressure is increased to 101.3 kPa?

  9. If a gas is found to have a volume of 200.0 mL at STP, what is the new pressure exerted on the gas if, the new volume of the gas is 400.0 mL?

  10. Charles Law • describes the effect that temperature (average kinetic energy) has on the volume of a gas • The volume of a mass of gas, at constant pressure, is directly proportional to its KELVIN temperature.

  11. Charles Law • The product of the volume divided by temp, in Kelvins,is a constant value. • BE SURE TO CONVERT ALL TEMPERATURES TO KELVIN WHEN WORKING WITH GASES • Therefore, the following equation is used to solve these problems: V1 = V2 T2 T2

  12. What volume will 240. mL of gas occupy if its temperature is raised from 27.0 ˚C to 127 ˚C, without changing pressure?

  13. If the temperature of 56.0 mL of gas is decreased from 273 ˚C to 0˚ C, without changing the pressure of the gas, what will the new volume of the gas be?

  14. Gay – Lussac’s Law • describes the relationship between the temperature and pressure of a gas, keeping the number of particles and volume constant. • The pressure and the Kelvin temperature of a mass of gas are directly proportional to one another, provided the volume remains constant. P1 = P2 T1 T2

  15. Combined Gas Law • combines all 3 previous formulas into one equation P1V1 = P2V2 T1 T2 **If any of the variables are held constant in a problem, eliminate it from the combined gas law to solve the problem.

  16. What will the volume be if 42.0mL of a gas are changed from 220.kPa and 27 ˚C to 240 kPa and -123 ˚C?

  17. 40.0 mL of a gas are collected at 300.0 kPa and 87 C. When the pressure is increased to 400.0 kPa, the volume changed to 50.0 mL. What was the new temperature of the gas?

  18. If the temperature of 56.0 L of gas is decreased from 273 C to 0 C, without changing the pressure of the gas, what will the new volume of the gas be?

  19. Gas Test Tuesday!Do Now: A gas occupies a volume of 444 mL at 273K and 79.0 kPa. What is the final Kelvin temperature when the volume of the gas is changed to 1880 mL and the pressure is changed to 38.7 kPa? T2 = 566 K

  20. Avogadro’s hypothesis • relates the volume of a gas to the number of gaseous particles (moles)in a sample • The volume of a gas is directly proportional to the quantity of gaseous particles (moles). • we use the variable n to represent the number of moles of a substance

  21. Avogadro’s hypothesis • ** Equal volumes of gas at the same temperature and pressure contain equal numbers of molecules of gaseous particles. • One mole of gas occupies 22.4 L of space at STP. ( 1 mole = 6.022 x 1023 particles)

  22. What volume will 0.50 moles of gas occupy?

  23. How many liters of gas will 0.23 moles of gas occupy at STP?

  24. How many moles of helium occupy the Snoopy balloon for the Thanksgiving day parade, if it takes 425, 000 L of helium to fill it up at STP?

  25. How many moles of gas are in a 3.7 L balloon at STP?

  26. Ideal Gas Law • combines the variables that effect the volume of a gas into one mathematical relationship P V = n R T where R is the gas law constant R = 8.31 L kPaOR R = 0.0821 L atm mol K mol K

  27. What is the pressure , in atmospheres exerted by 0.500 mol of nitrogen in a 10.0 L container at 298 K?

  28. A sample of helium has a volume of 500. mL at 20.3C and 90.5 kPa. Calculate the number of moles of this gas.

  29. What volume will 5.00 moles of CH4 occupy at 27⁰ C and 97.2 kPa? V = 128 L

  30. Which two samples of gas at STP contain the same total number of molecules? (1) 1 L of CO(g) and 0.5 L of N2(g) (2) 2 L of CO(g) and 0.5 L of NH3(g) (3) 1 L of H2(g) and 2 L of Cl2(g) (4) 2 L of H2(g) and 2 L of Cl2(g)

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