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KINETIC MOLECULAR THEORY

KINETIC MOLECULAR THEORY. Physical Properties of Gases:. Gases have mass Gases are easily compressed Gases completely fill their containers (expandability) Gases diffuse rapidly Gases exert pressure. Kinetic Molecular Theory. A theory that explains the physical properties

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KINETIC MOLECULAR THEORY

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  1. KINETICMOLECULARTHEORY

  2. Physical Properties of Gases: • Gases have mass • Gases are easily compressed • Gases completely fill their containers (expandability) • Gases diffuse rapidly • Gases exert pressure

  3. Kinetic Molecular Theory A theory that explains the physical properties of gases by describing the behavior of the particles

  4. KMT has 5postulates:

  5. #1 A gas consists of very small particles that have mass. (molecules or atoms)

  6. #2 Gas particles are very far apart from each other. (therefore gases are easily compressed)

  7. #3 Gas particles are in continuous, rapid, random motion.

  8. #4 Collisions of gas particles (with each other and with container) are perfectly elastic (no energy lost)

  9. #5 The average energy of the gas particles depends on the temperature of the gas.

  10. Measuring gases • Experimental work in chemistry requires measurements of quantities . Like volume, temperature, pressure and amount. This quantities are variables.

  11. We can measure gases in 4 ways:

  12. Temperature (T) A measurement of the average kinetic energy of a substance, the temperature is related with speed of the molecules of the gas.

  13. Higher temperatures cause gas particles to move faster

  14. K = °C + 273 14°C = ? K 14°C + 273 = 287K To solve gas problems, the temp must always be in Kelvin (K) !!!

  15. Pressure (P) The force per unit area on a surface

  16. Pressure is caused by gas particles slamming into the container’s walls.

  17. When pressure increases, the number of collisions in a determine time increases also

  18. VOLUME (V) • The volume of the gas is the same as the volume of the container. The unit is the Liter (L) = 1000cm3

  19. Units of Pressure: 1) atmosphere (atm) 2) Pascal (Pa) 3) millimeters of Mercury (mm Hg) 4) Torr 5) Pounds per square inch (lb/in2) 1 atm = 101,325 Pa 1 atm= 760 mm Hg = 760 torr 1 atm = 14.70 lb/in2 Bar = 100,000 Pa = 0.9869

  20. Amount of gas • The mole is the unit for specifying the amount of a sample of matter. You can relate the number of moles and the mass to the number of gas particles.

  21. The pressure exerted by air in the atmosphere is called atmospheric pressure. • VIDEO 1 Weather and air pressure • VIDEO 2 What is weather?

  22. Learning Check A. What is 475 mm Hg expressed in atm? 1) 475 atm 2) 0.625 atm 3) 3.61 x 105 atm B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? 1) 2.00 mm Hg 2) 1520 mm Hg 3) 22,300 mm Hg

  23. Solution A. What is 475 mm Hg expressed in atm? 485 mm Hg x 1 atm = 0.625 atm (B) 760 mm Hg B. The pressure of a tire is measured as 29.4 psi. What is this pressure in mm Hg? 29.4 psi x 1.00 atm x 760 mmHg = 1.52 x 103 mmHg 14.7 psi 1.00 atm (B)

  24. Enclosed Gases • If the container is closed, the pressure inside the container may be different from the atmospheric pressure. • Manometer: Instrument to measure the pressure in a closed container.

  25. Determining the pressure in the container will depend on the levels of the Hg on the two sides. • Pressure of the gas in the container is the same as the atmosphere WHEN THE TWO LEVELS ARE EQUALY HIGH • If the level of mercury is LOWER on the container side, the pressure in the container is higher than atmosphere.

  26. The difference between pressures in mmHg is simply the difference between the heights of the two columns. • To find the pressure of the gas in the container you must add or subtract the difference in pressures to the atmospheric pressure, witch you have separately determined by using a barometer.

  27. If the mercury level in the container is HIGHER that atmospheric side, the pressure in the container is less than the atmospheric pressure.

  28. WHEN THE GAS PRESSURE IS HIGHER THAN ATMOSPHERE PRESSURE, THE LEVEL OF MERCURY ON THE SIDE OF THE GAS WILL BE LOWER THAN OPEN ENDED SIDE. Add differences • WHEN GAS PRESSURE IS LOWER THAN ATMOSPHERIC PRESSURE, THE LEVEL ON THE SIDE OF THE GAS WILL BE HIGHER THAN OPEN ENDED SIDE.. • Subtract differences

  29. Pcontainer = Height difference – Atmospheric pressure • Pcontainer = Height difference + Atmospheric pressure

  30. STOP…collaborate and listen

  31. THE GAS LAWS • Mathematical representation of the observed relationships among the 4 variables • BOYLE’S LAW : The pressure- volume Famous experiment involved trapping air, changing its pressure , and measuring its volume. If the temperature remains unchanged the product of the pressure times the volume have a constant value K.

  32. PV = K • The pressure and volume of a sample of gas at constant temperature are inversely proportional to each other. • IF PRESSURE INCREASES, VOLUME DECREASES • IF VOLUME INCREASES, PRESSURE DECREASES • At same temperature the product of the pressure times the volume of a sample is always the same.

  33. Boyle’s Law P1V1 = P2V2 1 = trial 1 2 = after (trial 2) MUST BE AT CONSTANT TEMPERATURE!!

  34. A gas occupies a volume of 0.458 L at a pressure of 1.01 kPa and temperature of 295 Kelvin. Although the temperature stays the same, the volume is increased to 0.477 L. What is the new pressure? 0.970 kPa

  35. Charles’ Law • The relationship between volume gas and its temperature while the pressure and the amount of gas were held constant • VOLUME INCREASES AS TEMPERATURE INCREASES • V= K2 T • At constant pressure the volume of a fixed amount of gas is directly proportional to its absolute temperature.

  36. Charles’ Law V1T2 = V2T1 1 = before 2 = after MUST BE AT CONSTANT PRESSURE!!

  37. What will be the volume of a gas sample at 309 K if its volume at 215 K is 3.42 L? Assume that pressure is constant. 4.92 L

  38. Gay-Lussac’s Law 1 = before 2 = after MUST BE AT CONSTANT VOLUME!!

  39. A balloon with a pressure of 0.900 atm is heated from 105 K to 155 K. If volume is held constant, what is the new pressure? 1.33 atm

  40. Combined Gas Law 1 = before 2 = after JUST HOLD ONE QUANTITY CONSTANT!! (take it out of the equation)

  41. The gas in a 0.010 L container has a pressure of 1.39 atmospheres. When the gas is transferred to a 0.017 L container at the same temperature, what is the pressure of the gas? 0.82 atm

  42. The gas inside a 70.8 mL piston has a temperature of 35.0°C. If the temperature is raised to 100.0°C, what is the new volume of the gas? 85.7 mL

  43. An elastic container is inflated to a volume of 18.0 liters at a pressure of 1.26 atm. The container then expands to a new volume at a pressure of 1.05 atm. What is the new volume? 21.6 liters

  44. Avogadro’s Law The amount- volume relationship Equal volumes of gas (at same P and T) contain the same amount of particles

  45. It states that all gases show the same physical behavior • A gas with a larger volume must consist of a greater number of particles. As long as the pressure and temperature do not change • If the amount of gas increases the volume increases • If the amount of gas decreases the volume decreases

  46. 1 mole = 6.02 x 1023 particles 1 mole = 22.4 L Only works at same P and T V = K n

  47. Ideal Gas Law The mother of all gas laws. It includes everything! PV = nRT

  48. PV = nRT P = pressure (atm) V = volume (L) n = moles (mol) R = Gas Constant T = Temperature (Kelvin)

  49. PV = nRT MUST USE THESE UNITS!!!

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