2Section 13.1: Nature of Gases Kinetic Theory and a Model for GasesKinetic Energy: Energy that an object has because of its motionKinetic Theory: All matter consists of tiny particles that are in constant motionParticles in a gas are usually atoms/molecules.There are three fundamentals to the kinetic theory of gases which we will review one by one.
3Kinetic TheoryParticles in a gas are considered to be small, hard spheres w/ insignificant volume.- a lot of empty space between particles- no attractive/repulsive forces b/wparticles- Motion of 1 particle is independentfrom the motion of other particles
4Kinetic TheoryMotion of particles in a gas is rapid, constant and random- a gas will fill the shape of any container- uncontained gas spreads out with no limit- gas particles will travel in a straight path until they collide with something elseWhy would individuals in Mexico not be able to smell pizza from a shop in Washington D.C? (Oxygen molecules can travel 1700 km/h at 20 degrees Celsius)
5Kinetic TheoryAll Collisions between particles in a gas are perfectly elastic- Elastic Collision-Total kinetic energy remains constant between 2 molecules.-No K.E. is lost, only transferredExample:How does the following steel ball toy work?
7Components of Dry Troposphere Air SubstanceFormulaPercent of All Gas MoleculesMajor ComponentsNitrogen and OxygenN2O278%21%Minor ComponentsArgonCarbon DioxideArCO2.93%.033%Trace AmountsNeNH3HeCH4.0018%.0010%.0005%.0002%
8Atmospheric Pressure -What is atmospheric pressure? Results from the collisions of atoms and molecules in air with objectsAir exerts pressure on earth b/c gravity holds particles in the atmosphere.As you climb higher up amountain, does atmosphericpressure increase ordecrease and why?
9Athletes and Higher Altitude Athletes and trainers often recommend high altitude training as a means to increase exercise endurance. At higher altitudes, less oxygen results in the heart working harder.
10Atmospheric PressureHow much pressure are you under? Earth's atmosphere is pressing against each square inch of you with a force of 1 kilogram per square centimeter (14.7 pounds per square inch). The force on 1,000 square centimeters (a little larger than a square foot) is about a ton!Why doesn't all that pressure squash me? Remember that you have air inside your body too, that air balances out the pressure outside so you stay nice and firm and not squishy.
11Atmospheric Pressure Why do my ears pop? . As the number of molecules of air around you decreases, the air pressure decreases. This causes your ears to pop in order to balance the pressure between the outside and inside of your ear.Since you are breathing fewer molecules of oxygen, you need to breathe faster to bring the few molecules there are into your lungs to make up for the deficit.
12Measuring Pressure Barometer: used to measure atmospheric pressure The SI units of pressure is Pascal (Pa)other units: Millimeters of Mercury (mm Hg)atmospheres (atm1 atm = 760 mm Hg = kPaOld Mercury Barometer Is Shown to the Left.Atmospheric pressure depends on weather and altitude.
13Gas PressureGas Pressure: result of simultaneous collisions of billions of rapidly moving particles in a gas with an object.Vacuum: No pressure and No ParticlesWhy is there no pressure with no particles?Demonstration: Write a description of what is happening to the marshmallows
14Gas Activity Kinetic Molecular Theory Gas particles are small hard spheres with insignificant volume, -far apartGas particles move in a random, rapid and constant motionAll collisions between gas particles are perfectly elastic
15Properties of Gases Compressibility : is the measure of how much the volume of matter decreasesunder pressure.Why can gases be compressed?Because of the empty space between gas particles. At room temp; distance b/w particles in an enclosed gas is 10 x the diameter of the particle.Why does a collision with an inflated air bag cause much less damage than a collision with a steering wheel?When a person collides with an air bag, the impact forces the molecules of gas to compress, which absorbs the energy of the impact.
16V T P Four Variables Describe a Gas Pressure (P) in Kilopascals Temperature (T) in KelvinVolume (V) in LitersNumbers of Moles (n)Factors Affecting Gas Pressure-gas-volume- temperature
17Amount of GasIncrease the number of particles, increase number of collisions which leads to greater air pressure
18Volume How do you think volume will affect gas pressure? Increase the volume, decrease the pressure.More volume gives the molecules more space to travel around and frequency of collisions is less
19How does an Aerosol Can Work? Pressure in the can is higherthan the outside pressure.When the valve opens,the air will rush outtowards the lower pressureAir will travel from higherpressure to lower pressure
20Gas LawsBoyles Law: for a given mass of gas at constant temperature; the volume of gas varies inversely with pressureMathematical Expression of Boyles Law:P1 × V1 = P2 × V2
22P1 x V1 = P2 x V2 P1 = 726 mmHg P2 = ? V1 = 946 mL V2 = 154 mL P1 x V1 A sample of chlorine gas occupies a volume of 946 mL at a pressure of 726 mmHg. What is the pressure of the gas (in mmHg) if the volume is reduced at constant temperature to 154 mL?P1 x V1 = P2 x V2P1 = 726 mmHgP2 = ?V1 = 946 mLV2 = 154 mLP1 x V1V2726 mmHg x 946 mL154 mL=P2 == 4460 mmHg
23Graphing: Boyle’s Law Prepare the following graph X axis = volume (L), intervals of .5,0 to 4Y axis = pressure (kPa) intervals of 25,0 to 200Plot the following point : Pressure(P1) = 200, Volume(V1) = .5Using the equation : P1 × V1 = P2 × V2Solve for P2 in the table to the right, and thenplot all of the points from the table on your graph.P2V211.522.53
24Kinetic Energy and Temperature What’s the difference between Heat and Temperature?Heat = EnergyTemperature = measurement of heatWhen a substance is heated, its particles absorb energy- some is stored as P.E.The rest of the energy speeds up the particles and increases K.E.The faster the particles move, the higher the temperature!
25TemperatureWhy are an aerosol cans considered extremely flammable and dangerous if heated?An increase in temperature of an enclosed gas causes an increase in its pressure.If an aerosol can is thrown in a fire, the pressure increases so dramatically because of the heat, the can explodes
26Kinetic TheoryAll atoms and particles are in constant motion, however, is it possible for particles to have absolutely no motion?Absolute Zero is the temperature at which the motion of particles theoretically ceases. ( degrees C)Absolute Zero has never been produced in a laboratory, but scientists have been close
27Charles’s Law: Temp and Vol. Charles’s Law: states that the volume of a fixed mass of gas is directly proportional to its Kelvin temperature if the pressure is kept constant.Reminder Celsius to Kelvin, degrees.Mathematical RepresentationV1 = V2T T2
29V1/T1 = V2/T2 V1 = 3.20 L V2 = 1.54 L T1 = 398.15 K T2 = ? V2 x T1 V1 A sample of carbon monoxide gas occupies 3.20 L at 125 0C. At what temperature will the gas occupy a volume of 1.54 L if the pressure remains constant?V1/T1 = V2/T2V1 = 3.20 LV2 = 1.54 LT1 = KT2 = ?V2 x T1V11.54 L x K3.20 L=T2 == 192 K
30Graphing Charles Law Prepare the following graph T1 T2 T2 (x)V2 (y)30011.522.53Prepare the following graphX axis = temperature (K), intervals of 100, to 1000Y axis = Volume (L) intervals of 10 to 4Plot the following point : Volume = 1, Temp = 300 KPlot the rest of the graph by completing the followingcalculations using : V1 = V2T T2
31How does a hot air balloon work? Hot air is lighter than cold air, which makes the balloon float.
32Gay-Lussac’s Law:States that the pressure of a gas is directly proportional to the Kelvin temperature if the volume remains constant.Mathematical RepresentationP1 = P2T T2Example: The gas in a used aerosol can is at a pressure of 103 kPa at 25 degrees Celsius. If the can is thrown into a fire, what is the pressure at 928 degrees Celsius.
33Why should you never measure the pressure of your tires after a long trip? After a long trip, the air in yourtires heats up which increasesthe pressure.Tire inflation pressures fluctuate with changes in the outside air temperature. This occurs at a rate of about 1 psi for every 10°F (plus or minus).If you add the variations of time and temperature together, it is easy to understand why a tire's inflation pressure should be checked frequently. Improper inflation can cause tires to wear irregularly
34Summary of Three Gas Law’s RELAT-IONSHIPCON-STANTBoyle’sP VP1V1 = P2V2T, nCharles’V TV1/T1 = V2/T2P, nGay-Lussac’sP TP1/T1 = P2/T2V, n
35Combined Gas LawSingle expression that combines all of the previous gas laws into one.The combined gas law allows you to do calculations for situations in which only the amount of gas is constantMathematical Expression:P1 V P2P1×V1 = P2×V2T T2=T T2
36Combined Gas Law Problem A sample of helium gas has a volume of L, a pressure of atm and a temperature of 29°C. What is the new temperature of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?