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The Behavior of Gases Chapter 14

Concepts to consider. The Behavior of Gases Chapter 14. Kinetic Theory. Gases consist of hard spherical particles Particles have insignificant volume Large distance between particles No attractive or repulsive forces between particles Constant, random motion with elastic collisions.

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The Behavior of Gases Chapter 14

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  1. Concepts to consider The Behavior of GasesChapter 14

  2. Kinetic Theory • Gases consist of hard spherical particles • Particles have insignificant volume • Large distance between particles • No attractive or repulsive forces between particles • Constant, random motion with elastic collisions

  3. Variables and Equations • 4 variables are pressure (P) in kilopascals, temperature (T) in kelvins, volume (V) in liters, and number of moles (n). • Help to understand everyday applications such as airbags, scuba-diving equipment, and hot-air balloons.

  4. Compressibility • Why are gases compressed more easily than liquids or solids? • How does the overall volume of the particles in a gas compare to the overall volume of the gas? • How does an airbag work?

  5. Amount of a Gas • What happens to the pressure if you double the amount of particles in a rigid container? • How does an aerosol can work?

  6. Volume • If you double the volume of a rigid container, what can be said about the pressure? • What about if you halve the volume?

  7. Temperature • When you increase the temperature of gas molecules in a container, what happens to the pressure? • when molecules gain more KE and move faster, what happens to pressure? • If you leave a bag of potato chips in the sun, why will the bag start to bulge?

  8. Gas Laws • Boyle’s Law • Charles’ Law • Gay-Lussac’s Law • Combined Gas Law • Ideal Gas Law • Dalton’s Law • Graham’s Law

  9. Boyle’s Law • As volume increases, pressure _________. • Therefore, volume and pressure are inversely related • We can show this by P1V1 = P2V2

  10. Charles’ Law • As temperature increases, volume _________. • Therefore temperature and volume are directly related. • We can show this V1/T1 = V2/T2

  11. Gay-Lussac’s Law • As the pressure of an enclosed gas increases, the temperature __________. • Therefore temperature and pressure are directly related. • We can show this by P1/T1 = P2/T2

  12. The Combined Gas Law • We can combine the previous three laws into one law that involves P, T and V. • The combined gas law is written as P1V1 = P2V2 T1 T2

  13. The Ideal Gas Law • To calculate the number of moles of a contained gas, we use the variable ‘n’ • The ideal gas law is PV = nRT • R is known as the ideal gas constant • R = 8.31 (if pressure is in kPa) R = 0.0821 (if pressure is in atm)

  14. Ideal Gas Law • PV = nRT • What are the units on R? • Can we derive the value for R? • Remember that at STP, T = 273 K, P = 101.3 kPa, n = 1 mol, V = 22.4 L

  15. Ideal vs. Real • Real gases differ most from an ideal gas at low temperatures and high pressures • Remember, in reality, there are attractive forces between molecules

  16. Dalton’s Law • Also known as the law of partial pressures: In a mixture of gases, the total pressure is the sum of the partial pressures of the gases • Simply, Ptotal = P1 + P2 + P3 + … Pn • Why would a climber at the top of Mt. Everest care about Dalton’s Law?

  17. Graham’s Law • Gases with a lower molar mass will diffuse faster than gases with a larger mass • It makes sense that a lighter object will have to move faster to have the same energy as a larger object moving slowly • We can show this law as:

  18. How to Solve Problems Here is a sample problem: 5 moles of gas is heated to 400K in a 2.5 L container. What is the pressure of the gas? • Identify and write down variables. n = 5, T = 400K, V = 3.5 L

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