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To learn about atmospheric pressure and how barometers work To learn the units of pressure To understand how the pressure and volume of a gas are related To do calculations involving Boyles Law To learn about absolute zero To understand how the volume and temperature of a gas are related To do calculations involving Charless Law To understand how the volume and number of moles of a gas are related To do calculations involving Avogadros Law Objectives 13.1Describing the Properties of GasesGases 1Properties of GasesIn organized soccer, a ball that is properly inflated will rebound faster and travel farther than a ball that is under-inflated. If the pressure is too high, the ball may burst when it is kicked. You will study variables that affect the pressure of a gas.

Gases 2CompressibilityCompressibilityWhy are gases easier to compress than solids or liquids are?Gases 3CompressibilityCompressibility is a measure of how much the volume of matter decreases under pressure. When a person collides with an inflated airbag, the compression of the gas absorbs the energy of the impact.

Gases 4A crash dummy can be used to test the effectiveness of an air bag. Because gases can be compressed, the air bag absorbs some of the energy from the impact of a collision. Air bags work best when combined with seat belts.

CompressibilityGases are easily compressed because of the space between the particles in a gas.The distance between particles in a gas is much greater than the distance between particles in a liquid or solid.Under pressure, the particles in a gas are forced closer together.Gases 5Factors Affecting Gas PressureFactors Affecting Gas PressureWhat are the three factors that affect gas pressure?Gases 6Factors Affecting Gas PressureThe amount of gas, volume, and temperature are factors that affect gas pressure.Gases 7Factors Affecting Gas PressureFour variables are generally used to describe a gas. The variables and their common units arepressure (P) in kilopascalsvolume (V) in literstemperature (T) in kelvinsthe number of moles (n).Gases 8Factors Affecting Gas PressureAmount of GasYou can use kinetic theory to predict and explain how gases will respond to a change of conditions. If you inflate an air raft, for example, the pressure inside the raft will increase.Gases 9Factors Affecting Gas PressureCollisions of particles with the inside walls of the raft result in the pressure that is exerted by the enclosed gas. Increasing the number of particles increases the number of collisions, which is why the gas pressure increases.

Gases 10The volume of this air-filled raft is much larger than its volume before it was inflated. Using a pump to force air into a raft increases the pressure of the air inside the raft. The increased pressure causes the raft to inflate to its intended size.Factors Affecting Gas PressureIf the gas pressure increases until it exceeds the strength of an enclosed, rigid container, the container will burst.

Gases 11When a gas is pumped into a closed rigid container, the pressure increases as more particles are added. If the number of particles is doubled, the pressure will double. Predicting What would happen to the pressure in the container if the number of particles were tripled? If the number of particles were cut in half?Factors Affecting Gas PressureAerosol Spray Paint

Gases 12 The pressure of the gas inside a new can of spray paint is greater than the air pressure outside the can. When gas rushes though an opening in the top of the can, it propels, or forces, paint out of the can. As the can is used, the pressure of the propellant decreases. Relating Cause and Effect What happens when the pressure of the propellant equals the air pressure outside the can?Factors Affecting Gas PressureVolumeYou can raise the pressure exerted by a contained gas by reducing its volume. The more a gas is compressed, the greater is the pressure that the gas exerts inside the container.

Gases 13Factors Affecting Gas PressureWhen the volume of the container is halved, the pressure the gas exerts is doubled.

Gases 14A piston can be used to force a gas in a cylinder into a smaller volume. When the volume is decreased, the pressure the gas exerts is increased. Interpreting Diagrams What happens to the gas pressure when the volume is reduced from 1 L to 0.5 L?Factors Affecting Gas PressureTemperatureAn increase in the temperature of an enclosed gas causes an increase in its pressure. As a gas is heated, the average kinetic energy of the particles in the gas increases. Faster-moving particles strike the walls of their container with more energy.Gases 15Factors Affecting Gas PressureWhen the Kelvin temperature of the enclosed gas doubles, the pressure of the enclosed gas doubles.

Gases 16An increase in temperature causes an increase in the pressure of an enclosed gas. The container can explode if there is too great an increase in the pressure.A. Pressure Barometer device that measures atmospheric pressureInvented by Evangelista Torricelli in 1643 Measuring Pressure

Gases 17A. Pressure Changing weather conditions Atmospheric Pressure

Gases 18A. Pressure Changing altitude Atmospheric Pressure

Gases 19A. Pressure 1 standard atmosphere = 1.000 atm = 760.0 mm Hg = 760.0 torr = 101,325 Pa Units of Pressure Gases 20A. Pressure A manometer measures the pressure of a gas in a container. Units of Pressure

Gases 21B. Pressure and Volume: Boyles Law Robert Boyles experiment

Gases 22B. Pressure and Volume: Boyles Law

Gases 23B. Pressure and Volume: Boyles Law Graphing Boyles results

Gases 24B. Pressure and Volume: Boyles Law This graph has the shape of half of a hyperbola with an equation PV = k Volume and pressure are inversely proportional. If one increases the other decreases.

Gases 25Boyles Law: Pressure and Volume

Gases 26The pressure of a gas changes as the volume changes. INTERPRETING GRAPHS a. Observing When the volume is 2.0 L, what is the pressure? b. Predicting What would the pressure be if the volume were increased to 3.0 L? c. Drawing Conclusions Based on the shape of the graph, describe the general pressure-volume relationship.B. Pressure and Volume: Boyles Law Another way of stating Boyles Law isP1V1 = P2V2 (constant temperature and amount of gas)Gases 27As the temperature of the water increases, the volume of the balloon increases.

C. Volume and Temperature: Charless Law Gases 28When the gas in the blue balloon is cooled at constant pressure, the volume of the gas decreases. When the gas is heated at constant pressure, the volume increases. Calculating What is the ratio of volume to temperature for each set of conditions? Round your answer to two significant figures.C. Volume and Temperature: Charless Law Graphing data for several gases

Gases 29C. Volume and Temperature: Charless Law It is easier to write an equation for the relationship if the lines intersect the origin of the graph.

Use absolute zero for the temperature Gases 30C. Volume and Temperature: Charless Law These graphs are lines with an equation V = bT (where T is in kelvins) Volume and temperature are directly proportional. If one increases the other increases. Another way of stating Charless Law is V1 = V2 T1 T2 (constant pressure and amount of gas)Gases 31D. Volume and Moles: Avogadros Law

Gases 32D. Volume and Moles: Avogadros Law Volume and moles are directly proportional. If one increases the other increases. V = an constant temperature and pressure Another way of stating Avogadros Law is V1 = V2 n1 n2 (constant temperature and pressure) Gases 33To understand the ideal gas law and use it in calculations To understand the relationship between the partial and total pressure of a gas mixture To do calculations involving Daltons law of partial pressures To understand the molar volume of an ideal gas To learn the definition of STP To do stoichiometry calculations using the ideal gas law Objectives 13.2Using Gas Laws to Solve ProblemsGases 34A. The Ideal Gas Law Boyles Law V = k (at constant T and n) P Charless Law V = bT (at constant P and n) Avogadros Law V = an (at constant T and P)

We can combine these equations to get Gases 35A. The Ideal Gas Law Rearranging the equation gives the ideal gas law PV = nRTR = 0.08206 L atm mol K Gases 36B. Daltons Law of Partial Pressures What happens to the pressure of a gas as we mix different gases in the container? Gases 37B. Daltons Law of Partial Pressures Daltons law of partial pressures For a mixtures of gases in a container, the total pressure exerted is the sum of the partial pressures of the gases present. Ptotal = P1 + P2 + P3 Gases 38The partial pressure of oxygen must be 10.67 kPa or higher to support respiration in humans. The climber below needs an oxygen mask and a cylinder of compressed oxygen to survive.

B. Daltons Law of Partial Pressures Gases 39This climber is using a tank of compressed gas to supplement the supply of oxygen available at high altitudes.

B. Daltons Law of Partial Pressures The pressure of the gas is affected by the number of particles. The pressure is independent of the nature of the particles.

Gases 40B. Daltons Law of Partial Pressures Two crucial things we learn from this are: The volume of the individual particles is not very important. The forces among the particles must not be very important. Gases 41B. Daltons Law of Partial Pressures Collecting a gas over water Total pressure is the pressure of the gas + the vapor pressure of the water.

Gases 42B. Daltons Law of Partial Pressures Collecting a gas over water How can we find the pressure of the gas collected alone?

Gases 43C. Gas Stoichiometry Molar Volume Molar volume of an ideal gas at STP 22.4 L Standard temperature and pressure (STP)0oC and 1 atm For one mole of a gas at STP

Gases 44Grahams LawDiffusion is the tendency of molecules to move toward areas of lower concentration until the concentration is uniform throughout.Gases 45Grahams LawBromine vapor is diffusing upward through the air in a graduated cylinder.

Gases 46The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?Grahams LawAfter several hours, the bromine has diffused almost to the top of the cylinder.

Gases 47The diffusion of one substance through another is a relatively slow process. a) Bromine vapor is diffusing upward through the air in a graduated cylinder. b) After several hours, bromine vapors are near the top of the cylinder. Predicting What will happen as the bromine continues to diffuse?Grahams LawDuring effusion, a gas escapes through a tiny hole in its container. Gases of lower molar mass diffuse and effuse faster than gases of higher molar mass.Gases 48Grahams LawThomas Grahams ContributionGrahams law of effusion states that the rate of effusion of a gas is inversely proportional to the square root of the gass molar mass. This law can also be applied to the diffusion of gases.Gases 49Grahams LawComparing Effusion RatesA helium filled balloon will deflate sooner than an air-filled balloon.

Gases 50The character balloons used in parades are filled with helium gas so that they will float.

Grahams LawHelium atoms are less massive than oxygen or nitrogen molecules. So the molecules in air move more slowly than helium atoms with the same kinetic energy.Gases 51Grahams LawBecause the rate of effusion is related only to a particles speed, Grahams law can be written as follows for two gases, A and B.

Gases 52Grahams LawHelium effuses (and diffuses) nearly three times faster than nitrogen at the same temperature.

Gases 53To understand the relationship between laws and models (theories) To understand the postulates of the kinetic molecular theory To understand temperature To learn how the kinetic molecular theory explains the gas laws To describe the properties of real gases Objectives 13.3Using a Model to Describe GasesGases 54A. Laws and Models: A Review

Gases 55A. Laws and Models: A Review A model can never be proved absolutely true. A model is an approximation and is destined to be modified. Gases 56B. The Kinetic Molecular Theory of Gases

Gases 57C. The Implications of the Kinetic Molecular Theory Meaning of temperature Kelvin temperature is directly proportional to the average kinetic energy of the gas particles Relationship between Pressure and Temperature gas pressure increases as the temperature increases because the particles speed up Relationship between Volume and Temperature volume of a gas increases with temperature because the particles speed up Gases 58D. Real Gases Gases do not behave ideally under conditions of high pressure and low temperature. Why? Gases 59D. Real Gases At high pressure the volume is decreased Molecule volumes become important Attractions become important

Gases 60