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Behavior of Gases & Kinetic Molecular Theory

Unit 7 – Phase of Matter. Behavior of Gases & Kinetic Molecular Theory. Characteristic Properties of Gases. Volume – a gas does not have a definite shape or volume . The volume depends on the container size, room temperature and pressure.

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Behavior of Gases & Kinetic Molecular Theory

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  1. Unit 7 – Phase of Matter Behavior of Gases&Kinetic Molecular Theory

  2. Characteristic Properties of Gases • Volume– a gas does not have a definite shape or volume. The volume depends on the container size, room temperature and pressure. • Expandability- gases will expand to fit any size container. Increasing temperature will cause the gas to expand thereby increasing volume and pressure in the container.

  3. Characteristic Properties of Gases • Compressibility-the volume of a gas can be decreased by increasing the pressure.

  4. Low Density-because the particles in a gas are so far apart and density is mass per unit volume, it makes sense that gases occupy roughly 1000 times more volume than the same amount of substance as a liquid or solid . • Gases are mostly empty space!

  5. Diffusion and Effusion • Diffusion is the spontaneous mixing of the particles of two different gases. • Effusion is the process where gas particles under pressure will pass through a tiny opening

  6. Graham’s Law The rate of effusion and diffusion is inversely proportional to the square root of the molar mass of the molecules. The lower the molar mass, the faster the gas molecules are at a set temperature! RateA Molar MassB RateB  Molar MassA =

  7. Graham’s Law of Effusion/Diffusion Why does reaction “white cloud appear closer to the HCl side? HCl has a higher molecular weight than NH3 and therefore moves slower!

  8. Kinetic-Molecular Theory 1. Gases consist of tiny particles (atomsor molecules) that are far apart relative to their size. • The particles have an insignificant volume 2. Gas particles are in constant random motion. They therefore possess kinetic energy defined as KE = ½ (mass)(velocity)2 • More energy = faster particles

  9. Kinetic-Molecular Theory 3. There are no forces of attractionor repulsion between the particles. 4. Collisions between gas particles and between particles and the container are elastic. (no net loss of kinetic energy).

  10. Kinetic Molecular Theory 5. The average kinetic energy of gas particles depends on the temperature of the gas. • Higher temperature means more energy and faster particles

  11. Pressure Force = (mass)(acceleration) Which shoes create the most pressure?

  12. Pressure • Gas Pressure is created by the collisionsof gas particles with a surface. • In general – more collisions = higher pressure and less collisions = lower pressure

  13. Units of Pressure • Pascal (Pa) • 1Pa = 1 newton/m2 • Millimeters of Mercury (mmHg) • Pressure that supports a 1mm mercury column in barometer.

  14. Pressure Mercury Barometer • Barometer • measures atmospheric pressure in mmHg Standard Pressure at sea level = 760mmHg

  15. Pressure U-tube Manometer • Manometer • measures contained gas pressure

  16. Pressure Units • Atomosphere (atm) • Average atmospheric pressure at sea level at 0oC = 1atm • Torr • Another name for millimeters of mercury • 1 torr = 1mmHg

  17. Pressure Units • KEY UNITS AT SEA LEVEL 1 atm = 760 mm Hg = 760 torr = 101.325 kPa (kilopascal) = 14.7 psi

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