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Gases

This article provides an overview of the characteristics of gases and the kinetic theory that describes their behavior. It covers the properties of gas particles, their constant motion, and perfectly elastic collisions. The variables that describe gases, such as pressure, volume, temperature, and moles, are explained. The article also discusses different units of pressure, atmospheric pressure, measurement techniques, and the relationship between pressure units. Additionally, it highlights the concept of vacuum and the standard temperature and pressure (STP). The importance of the Kelvin temperature scale in describing the movement of gas particles is emphasized.

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Gases

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  1. Gases Describing Gases

  2. Review of Kinetic Theory Particles in an ideal gas… • gases are hard, small, spherical particles • don’t attract or repel each other. • are in constant, random, straight-line motion. • indefinite shape and volume. • have “perfectly” elastic collisions.

  3. Variables that describe a gas Variables Units Pressure (P) – kPa, mm Hg, atm, torr L , mL , cm3 Volume (V) – °C , K (convert to Kelvin) K = °C + 273 Temp (T) – Mole (n) - mol

  4. Gas Pressure -collision of gas molecules with the walls of the container

  5. Atmospheric Pressure-collision of air molecules with objects

  6. Which shoes create the most pressure?

  7. U-tube Manometer Gas Pressure -- 3 ways to measure pressure: • atm (atmosphere) • mm Hg • kPa (kilopascals)

  8. Vacuum- empty space with no particles and no pressure Ex: space Atmospheric pressure is measured with a barometer. Increase altitude – decrease pressure Ex. Mt. Everest – atmospheric pressure is 253 mm Hg

  9. How pressure units are related: 1 atm = 760 mm Hg = 101.3kPa How can we make these into conversion factors? 1 atm101.3 kPa 760 mm Hg 1 atm

  10. Guided Problem: 1. Convert 385 mm Hg to kPa 385 mm Hg 2. Convert 33.7 kPa to atm 33.7 kPa 101.3 kPa x = 51.3 kPa 760 mm Hg x 1 atm = .33 atm 101.3 kPa

  11. STP Standard Temperature and Pressure Standard pressure – 1 atm, 760 mm Hg, or 101.3 kPa Standard temp. – 0° Celsius or 273 Kelvin

  12. Gases Kelvin Temperature Scale is directly proportional to the average kinetic energy, so Temperature is a description of the movement of particles (not how hot or cold it is)

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