Slide 1 / 140 Slide 2 / 140 Gases Slide 3 / 140 Slide 4 / 140 Table of Contents The Kinetic Molecular Click on the topic to go to that section Theory · The Kinetic Molecular Theory · Properties of Gases · Measuring Pressure · Gas Laws · Ideal Gas Law · Gas Density · Partial Pressure · Graham's Law of Effusion · Real versus Ideal Gases Return to Table of Contents Slide 5 / 140 Slide 6 / 140 Kinetic Molecular Theory The Kinetic-Molecular Theory In order to understand the behavior of gases, we work with some key premises. This revolutionary theory was developed by Ludwig Boltzmann in the late 1800's. It was based on the idea that matter is made up of atoms and molecules too small to be seen... ideas that were rejected by most scientists until the PREMISE 1 early 1900's...only a 100 years ago. Gas molecules are in constant motion and therefore possess kinetic energy. The faster the This theory connects the microscopic world of atoms and speed, the higher the kinetic molecules with the macroscopic world around us and helps us energy. greatly understand the behavior of gases.
Slide 7 / 140 Slide 8 / 140 Kinetic Molecular Theory Kinetic Molecular Theory PREMISE 2 PREMISE 2 (continued) The average kinetic energy The average kinetic energy of a of a sample of a gas is proportional to sample of a gas is proportional to the temperature. the temperature. Low Temperature The higher the temperature, the higher the average kinetic energy. Notice that at any given temperature, there is a wide range of speeds yet the average speed is clearly greater at the higher temperatures. High Temperature Slide 9 / 140 Slide 10 / 140 Temperature Temperature There are 3 scales used for measuring temperature. It is important that we can convert between the two scientific units used to measure ( F) (C) Celsius (K) Kelvin temperature (K and C) 212 100 373 H 2 O boiling point C + 273 = K or K - 273 = C 32 0 273 H 2 O freezing point So... a temperature of 16 C = 289 K Absolute zero -460 -273 0 *Absolute zero is the lowest theoretical temperature. Slide 11 / 140 Slide 11 (Answer) / 140 1 At the equator of Mars, the temperature can be quite 1 At the equator of Mars, the temperature can be quite balmly during the summer, reaching about 70 balmly during the summer, reaching about 70 Fahrenheit or 20 Celsius. What would this be in Fahrenheit or 20 Celsius. What would this be in Kelvin? Kelvin? A 253 K A 253 K Answer B -253 K B -253 K C C 293 K C 293 K D -293 K D -293 K E 32 K E 32 K [This object is a pull tab]
Slide 12 / 140 Slide 12 (Answer) / 140 2 Standard temperature is considered 273 K. What is 2 Standard temperature is considered 273 K. What is this temperature in Celsius? this temperature in Celsius? A 273 C A 273 C B 0 C B 0 C C -273 C C -273 C Answer B D 32 C D 32 C E 546 C E 546 C [This object is a pull tab] Slide 13 / 140 Slide 13 (Answer) / 140 3 Water freezes at about 0 degrees Celsius. At 3 Water freezes at about 0 degrees Celsius. At what absolute temperature does water freeze? what absolute temperature does water freeze? Answer 273 K Slide 14 / 140 Slide 14 (Answer) / 140 4 The average temperature of the universe is 4 The average temperature of the universe is thought to be roughly -270.5 Celsius. What is thought to be roughly -270.5 Celsius. What is that temperature in Kelvin? that temperature in Kelvin? Answer 2.5 K
Slide 15 / 140 Slide 15 (Answer) / 140 5 Room temperature is about 20 degrees Celsius. 5 Room temperature is about 20 degrees Celsius. What temperature is that in Kelvin? What temperature is that in Kelvin? Answer 293 K [This object is a pull tab] Slide 16 / 140 Slide 17 / 140 Kinetic Molecular Theory Kinetic Molecular Theory PREMISE 4 Kinetic Energy Before = = Kinetic Energy After Because of their extremely low density, we assume that the gas molecules occupy a negligible amount of space in a container. Therefore the volume of the PREMISE 3 Collisions between gas container is essentially the molecules are perfectly volume occupied by the gas. elastic, meaning that there is not net loss in kinetic energy over the course of the collision. Slide 18 / 140 Slide 19 / 140 Kinetic Molecular Theory Properties of Gases Premise Summary Statement Gas molecules are in constant motion and therefore 1 possess kinetic energy Average kinetic energy of gases is proportional to the 2 temperature 3 Collisions between gas molecules are elastic Gases occupy a negligible amount of space in the 4 container Return to Table of Contents
Slide 20 / 140 Slide 21 / 140 Characteristics of Gases Characteristics of Gases Since there are very few attractions between gas molecules.... The gaseous state is characterized by extremely weak interactions between the atoms, ions, and molecules. Gas molecules are free to move and will expand to fill their containers Gases (essentially no bonds) liquid same group same group of molecules of liquid gas molecules gas molecules molecules Solids (strong bonds) Liquids (weak bonds) liquids do not expand to fit their containers. Slide 22 / 140 Slide 23 / 140 Characteristics of Gases Characteristics of Gases Since there are very few attractions between gas molecules.... Since gases have such low densities, meaning very few molecules in a very large space, they can be compressed into a much smaller volume! A small number of molecules can occupy a large volume resulting in very low densities Physical State of Water Density (g/mL) Ice 0.91 g/mL Liquid 0.98 g/mL Vapor (gas) 0.00052 g/mL A turbocharger compresses the air before it enters the car or jet engine. Note the gas is over 1800 times less dense than the liquid! Slide 24 / 140 Slide 24 (Answer) / 140 6 Which of the following would NOT describe the 6 Which of the following would NOT describe the gaseous state of matter? gaseous state of matter? A High compressibility A High compressibility Strong intermolecular attractions Strong intermolecular attractions B B Answer Low Density Low Density C C B Will expand to fill container Will expand to fill container D D Particles are in motion Particles are in motion E E [This object is a pull tab]
Slide 25 / 140 Slide 25 (Answer) / 140 7 Which of the following would be TRUE regarding 7 Which of the following would be TRUE regarding the gaseous state? the gaseous state? A Gases are slightly less dense than the liquid state A Gases are slightly less dense than the liquid state Answer B Gases have attractive forces similar to that of the other states B Gases have attractive forces similar to that of the other states C The volume of a gas can change far more than that of a solid The volume of a gas can change far more than that of a solid C C or liquid or liquid Gas molecules weigh less than molecules in the liquid or solid Gas molecules weigh less than molecules in the liquid or solid D D state state None of these are true None of these are true E E [This object is a pull tab] Slide 26 / 140 Slide 26 (Answer) / 140 8 Which of the following is NOT true of gases? 8 Which of the following is NOT true of gases? A Gas molecules are in motion A Gas molecules are in motion At a given temperature, all of the gas molecules are At a given temperature, all of the gas molecules are B B moving at the same speed moving at the same speed Answer Gas molecules take up very little space in a Gas molecules take up very little space in a C C B container container The higher the temperature, the higher the average The higher the temperature, the higher the average D D kinetic energy of the gas molecules kinetic energy of the gas molecules The kinetic energy of a gas molecule before and The kinetic energy of a gas molecule before and E E after a collision is the same after a collision is the same [This object is a pull tab] Slide 27 / 140 Slide 28 / 140 Measuring Gases In order to understand gases, we measure Measuring Pressure four variables Pressure Temperature Volume Number of moles We will focus first in describing how we measure pressure and temperature before discussing the relationships between these four variables Return to Table of Contents
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