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Intro to Gases

Intro to Gases. The atmosphere is a mixture of many types of gases. Physical Properties of Gases. No definite shape or volume expand to fill & take shape of container Compressible Low Density air: 0.00117 g/cm 3 Exert uniform pressure on container walls Mix spontaneously and completely

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Intro to Gases

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  1. Intro to Gases

  2. The atmosphere is a mixture of many types of gases

  3. Physical Properties of Gases • No definite shape or volume • expand to fill & take shape of container • Compressible • Low Density • air: 0.00117 g/cm3 • Exert uniform pressure on container walls • Mix spontaneously and completely • diffusion

  4. Kinetic Theory • KT is used to explain the behavior of gases • KT is based on the assumption that all gases behave like the “ideal gas” • The “ideal gas” does not exist • It is a model used in an attempt to explain observations • If it did exist, what would it look like?

  5. Properties of an Ideal Gas • Particles move with constant velocity until they collide with something • Particles have no volume • No interaction between the particles • Collisions between particles are elastic (no loss of energy) • Particles move faster at higher temperatures

  6. Properties of an Ideal Gas • Particles of the gas move at a rapid, constant speed traveling in a straight line until the collide with some other object • Could be the wall of the container it’s in • Could be another gas particle

  7. Properties of an Ideal Gas • Particles of the gas are so small that the volume of the particles is essentially zero when compared to the volume that the gas occupies • Why can’t this be true? (think of what would happen if this gas condensed into a liquid)

  8. Properties of an Ideal Gas • There are no attractive or repulsive forces between the particles • Because gases are made of atoms, can this be true? • These forces are so small and the particles travel so quickly that it can be assumed that there is no interaction

  9. Properties of an Ideal Gas • Energy must be conserved in all collisions • It’s not so much the amount of energy, but the form in which it exists • Particles must maintain the same amount of kinetic energy • Travel just as fast before a collision as after • If this wasn’t true, gases would loose energy and condense on their own

  10. Properties of an Ideal Gas • The average kinetic energy (KE) of the particles is directly proportional to the temperature. • What effect does this have on the speed of the particles?

  11. Temperature • Temperature is a measure of the average KE of the particles • KE = ½ mv2

  12. Temperature • Heavier gases will, on average, travel more slowly than lighter gases at the same temperature, but with less variation in speed from particle to particle • At higher temperatures, there is more distribution in the speed of the individual particles, but the average KE is increased

  13. Temperature • Temperature must be given when discussing the behavior of a gas • It changes the average KE of the particles • This changes their behavior • Temperature must be absolute temperature (Kelvin Scale) • K = oC + 273

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