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Section 13.1

Section 13.1 . The Nature of Gases. Kinetic = Motion. The origin of the word kinetic means moving or motion. Condense. Freeze. sublimation. Evaporate. Melt. Gas . Liquid. Solid. Temperature . Physics Definitions A measure of average particle kinetic energy

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Section 13.1

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  1. Section 13.1 The Nature of Gases

  2. Kinetic = Motion • The origin of the word kinetic means moving or motion

  3. Condense Freeze sublimation Evaporate Melt Gas Liquid Solid

  4. Temperature • Physics Definitions • A measure of average particle kinetic energy • A measure of thermal energy. • Not dependent on mass.

  5. Kinetic Molecular Theory of Heat • Atoms held by electromagnetic forces • Atoms vibrate • Thermal energy is a measure of this motion. • More motion = more heat • Add heat = increase motion and thermal energy. • Think atoms: When heat or pressure is applied to a gas what happens to the molecules • More energy -> more collisions and more volume • More motion = more heat

  6. Conservation of Energy • Just like mass/matter energy cannot be created or destroyed • Law of Conversation of Energy: in a closed, isolated system energy cannot be created nor destroyed • Etotal= KE + PE • Energy can either change forms or be transferred to another object • Einitial= Efinal

  7. Kinetic Energy • So what happens when the object is released and begins to move? • The energy is transferred into another form of energy known as Kinetic Energy (KE). • Anytime an object is moving it has kinetic energy. Thus, kinetic energy depends on velocity. It also depends on mass. Units: J

  8. Thermometers are Speedometers

  9. Applying knowledge • Consider two samples of different gases. One sample consists of helium atoms and the other sample consists of diatomic oxygen molecules. If the samples are at the same temperature, will the particles within the sample have the same average speed?

  10. Answer • No • Temperature is a measure of the average kinetic energy of the samples. Translational kinetic energy depends upon both the mass of the particles and the average speed at which the particles move. In comparing two samples of different gases at the same temperature, the gas with the more massive particles has the slowest particle speeds. So in comparing the speeds of helium atoms and diatomic oxygen molecules, one must be conscious of the relative masses of the two particles. Helium particles, being roughly one-eighth the mass of diatomic oxygen molecules, will move with a considerably faster speed.

  11. Applying the Concepts • The particles in a sample of table salt (sodium chloride) are not free to move about. They are locked in place in a structure known as a crystal lattice. Can the particles of sodium chloride possess kinetic energy?

  12. Answer • Yes • Even though they do no possess any translational kinetic energy, they still possess some vibrational kinetic energy. The sodium and chloride ions can wiggle about their fixed lattice positions. The back and forth vibrational motion of the particles is what gives them vibrational kinetic energy. This explains why a thermometer will register a temperature when placed in the sample of matter.

  13. How does a thermometer work? • Liquid (usually an alcohol) encased in narrow glass tube • Liquid thermometers are based on the principal of thermal expansion • When a substance gets hotter, it expands to a greater volume. • As the temperature of the liquid in a thermometer increases, its volume increases.

  14. Gas Pressure Pressureis defined as force per unit area. Gas particles exert pressure when they collide with the walls of their container.

  15. Gas Pressure The particles in the earth’s atmosphere exert pressure in all directions called air pressure. There is less air pressure at high altitudes because there are fewer particles present, since the force of gravity is less.

  16. Gas Pressure Torricelli invented the barometer. Barometersare instruments used to measure atmospheric air pressure.

  17. Gas Pressure Manometers measure gas pressure in a closed container.

  18. Gas Pressure • The SI unit of force is the newton (N). • One pascal(Pa) is equal to a force of one Newton per square meter or N/m2. • One atmosphereis equal to 760 mm Hg or 101.3 kilopascals.

  19. Gas Pressure

  20. 1 Mole = 6.02x10^23 particles Avogadro’s principlestates that equal volumes of gases at the same temperature and pressure contain equal numbers of particles.

  21. STP – Standard Temperature and Pressure Avogadro's Principle (cont.) The molar volume of a gas is the volume 1 mol occupies at 0.00°C and 1.00 atm of pressure. 0.00°C and 1.00 atm are called standard temperature and pressure (STP). At STP, 1 mol of gas occupies 22.4 L.

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