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Chapter 13 Kinetic - Molecular Theory

Chapter 13 Kinetic - Molecular Theory. The Nature of Gases. The word “ Kinetic ” means motion The energy an object has due to its motion is called kinetic energy The kinetic theory states that tiny particles in all forms of matter are in constant motion !. The Nature of Gases.

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Chapter 13 Kinetic - Molecular Theory

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  1. Chapter 13Kinetic - Molecular Theory

  2. The Nature of Gases • The word “Kinetic” means motion • The energy an object has due to its motion is called kinetic energy • The kinetic theory states that tiny particles in all forms of matter are in constant motion!

  3. The Nature of Gases Three basic rules of the kinetic theory for gases: 1.Gas is made of particles- usually molecules or atoms • Small, hard spheres • Insignificant volume; relatively far apart from each other • No attraction or repulsion between particles

  4. The Nature of Gases 2.Particles in a gas move rapidly in constant random motion • Move in straight paths, changing direction only when colliding with something else • Average speed of O2 in air at 20 oC is an amazing 1660 km/h! • Random walk is a very short distance

  5. The Nature of Gases 3. Collisions are perfectly elastic • meaning kinetic energy is transferred without loss from one particle to another • the total kinetic energy remains constant • no energy is lost between particles

  6. The Nature of Gases Gas Pressure – defined as the force exerted by a gas per unit surface area of an object • Due to: a) force of collisions, b) number of collisions No particles present? Then there cannot be any collisions, and thus no pressure – called a vacuum

  7. The Nature of Gases Atmospheric pressure results from the collisions of air molecules with objects • Decreases as you climb a mountain because the air layer thins out as elevation increases Barometer is the measuring instrument for atmospheric pressure; dependent upon weather

  8. The Nature of Gases The SI unit of pressure is the “pascal” (Pa) • At sea level, atmospheric pressure is about 101.3 kilopascals (kPa) • Older units of pressure include 760 Torr 760 mmHg 14.7 psi 76 cmHg 1 atmosphere

  9. The Nature of Gases Mercury Barometer –a straight glass tube filled with Hg, and closed at one end; placed in a dish of Hg, with the open end below the surface • At sea level, the mercury would rise to 760 mm high at 25 oC- called one standard atmosphere (atm)

  10. The Nature of Gases As the atmospheric pressure outside pushes the Hg in the dish, the level raises in the tube and can be measured.

  11. The Nature of Gases For gases, it is important to relate measured values to standards: • Standard conditions for gases are a temperature of 0 oC and a pressure of 101.3 kPa, or 1 atm • This is called Standard Temperature and Pressure, or STP

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