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Kinetic Theory

Kinetic Theory. All matter consist of small particles. The molecules are in constant, random, rapid motion. All collisions are elastic (no net loss of energy). As temperature increases, the molecules’ velocity increases, increasing the pressure on the container. Mean free path.

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Kinetic Theory

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  1. Kinetic Theory • All matter consist of small particles. • The molecules are in constant, random, rapid motion. • All collisions are elastic (no net loss of energy).

  2. As temperature increases, the molecules’ velocity increases, increasing the pressure on the container.

  3. Mean free path • The average distance traveled between collisions • To calculate (for the curious) =(average speed)x(average time between collisions) An oxygen molecule will collide with other molecules 4.5 billion times per second!!

  4. The temperature of a substance is a measure of the average kinetic energy of its particles. Absolute zero- the temperature at which all molecular motion stops. -273.15°C

  5. Gas Pressure • Caused by gas molecules colliding with the sides of a container. • Force per unit area • Units: pascal= 1Newton/m2 1 atmosphere=101.325 kPa = 760 mm Hg (torr)

  6. How many mm Hg (or torr) is one kPa? 1.0 kPa x 760 mm Hg 101.325 kPa = 7.5 mm Hg

  7. Measuring Pressure • Open manometer- atmosphere exerts pressure on one side and gas sample exerts pressure on the other side. • Add, if gas pressure is greater • Subtract, if air pressure is greater • Closed manometer (barometer)- vacuum on one side, gas pressure on other side. • No addition or subtraction necessary

  8. States of Matter No No Definite Definite yes No Indefinite Definite Indefinite Indefinite yes yes

  9. Vapor pressure • The pressure produced when vapor particles above a liquid collide with the container walls; a dynamic equilibrium exists between the liquid and vapor. • Vapor pressure increases with temperature. • A substance with weak intermolecular forces has a high vapor pressure and low boiling point (volatile)- alcohols, ether. • A substance with strong intermolecular forces has a low vapor pressure and high boiling point (nonvolatile)- water, molasses, glycerol.

  10. Phase Diagram Critical point- above this temperature, no amount of pressure can liquefy it. Triple point- all three phases are at equilibrium

  11. “Normal” boiling and freezing points are those at standard pressure.

  12. Paraffin Water

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