Chapter 7 Gases Liquids amp Solids Appearance by Intermolecular Forces The Nature of Gases Indefinite shape and indefinite volume expand to fill their containers compressible Fluid they flow ID: 762879
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Chapter 7 Gases , Liquids, & SolidsAppearance by Intermolecular Forces
The Nature of Gases Indefinite shape and indefinite volume expand to fill their containers compressibleFluid – they flow Low density 1/1000 the density of the equivalent liquid or solid
Pressure Is caused by the collisions of molecules with the walls of a container Is equal to force/unit area P=F/A SI units = Newton/meter2 = 1Pascal (Pa) 101,325 Pa = 1 standard atmosphere (1atm)1 atm = 760mmHg = 760 torr = 14.7 psi
GAS LAWS Boyle ’s LawCharles’ Law Gay-Lussac’s LawAvogadro’sLawIdeal Gas LawDaltons Law
BOYLE ’S LAWThe Relationship Between Pressure and Volume
Robert Boyle (1627-1691) Boyle was born into an aristocratic Irish family Became interested in medicine and the new science of Galileo and studied chemistry. A founder and an influential fellow of the Royal Society of London Wrote prolifically on science, philosophy, and theology.
Boyle ’ s Law Boyle’s Law: The volume of a gas is inversely proportional to the pressure applied to the gas when the temperature is kept constant .Decrease in volume = Increase in pressure.Increase in volume = Decrease the pressure
Boyle ’s Equation: P 1V1 = P2V2Therefore:V1=(P2V2)/P1V2= ( P 1 V 1 )/ P 2 P 1 =( P 2 V 2 )/ V 1 P 2 =( P 1 V 1 )/ V 2
Problems You have a 2L cylinder of gas that is under 100 kPa of pressure. If you compress the gas to 1L, what will the new pressure be?You have a 10.0L container of gas under 505 torr of pressure. If you increase the pressure to 1155 torr, what will the new volume be?
The Relationship Between Temperature and Volume
Jaques Charles (1746-1823 ) Charles studied the compressibility of gases nearly a century after Boyle French Physicist Conducted the first scientific balloon flight in 1783
Charles ’ LawAt a fixed pressure, the volume of a gas is proportional to the temperature of the gas. As the temperature increases, the volume increases.As the temperature decreases, the volume decreases.
How Did He Figure It Out? A cylinder with a piston and a gas is immersed in a water bath. A mass is placed on top of the piston which results in a pressure on the gas. This mass is held constant, which means that the pressure on the gas is constant. The gas volume is measured as the temperature is increased and V vs. T data point plotted. This is continued over a large range of temperatures.
Charles’ EquationRearrange the equation to solve for V1, T1, V2, or T 2V1=(V2T1)/T2T1=(V1T2)/V2V2=(V1T2)/T1T2=(V 2T1)/V1All temperatures must be in KELVIN!!!
Problems A cylinder contains 5.00L of gas at 225K. If the temperature is increased to 345K, what will the new volume be?A tire contains 2.00L of air at 300.0K, if the volume in the tire decreased to 1.50L, what must the new temperature be? A ball contains 3.00L of air at 32.0ºF, if the volume increases to 5.00L, what must the temperature have changed to?
Gay-Lussac’s Law The Relationship Between Pressure and Temperature
Joseph Louis Gay-Lussac 1778 - 1850 French chemist and physicist Known for his studies on the physical properties of gases. In 1804 he made balloon ascensions to study magnetic forces and to observe the composition and temperature of the air at different altitudes
Gay-Lussac ’ s LawThe pressure of a fixed amount of gas at fixed volume is directly proportional to its temperature in Kelvin.As the temperature increases, the pressure also increasesAs the temperature decreases, the pressure also decreases
Gay-Lussac’s LawExpressed Mathematically as: Rearranging this equation to solve for the variables gives us:P1=(P 2T1)/T2P2=(P1T2)/T1T1=(P1T2)/P 2T2=(P2T1)/P1All temperatures must be in KELVIN!!!
Problems Jim Bob (he’s back) has revved his engine enough so that the internal temperature and pressure of his engine are 700.0K and 200.0kPa. If the temperature outside was 295K before Jim-Bob got into his car, what was the internal pressure in his engine?Today, the barometer reads 750mmHg and the thermometer says that it is 65ºF. At 6am, the barometer read 700mmHg, what was the temperature at that time?
The Combined Gas Law The Relationship Between Pressure, Volume, and Temperature
The Combined Gas LawA combination of Boyle’s, Charles’, and Gay-Lussac’s laws. Temperature must be in KELVIN.
Rearranged to solve for each variable:P1=(P2V2T1)/(V1T2)V 1=(P2V2T1)/(P1T2)T1=(P1V1T2)/(P2V2)P2=(P1V1T2 )/(V2T1)V2=(P1V1T2)/(P2T1)T2=(P2V2T1)/(P1V1)
ProblemsRhonda’s helium balloon has a volume of 2.00L at 2.00atm and 395K. If the temperature is raised to 500.K and the gas is compressed to 1.00L, what is the new pressure? Ryan ate at Taco Shack last night. He now has gas which takes up 1.29L of bowel space under 2.35atm of pressure at 310K (body temp). What will be the volume of Jeremy’s gas after he expels it if the atmospheric temperature and pressure are 75ºF and 1.00atm respectively?
Avogadro ’s Law The Relationship Between Pressure, Temperature, Volume and Moles
Amedeo Avogadro(1776-1856)Italian physicist and mathematicianBorn in a noble ancient family of Piedmont“Avogadro’s Number ” is named after him6.022 x 1023The number of things in a mole
Avogadro ’s Law One mole of any gas occupies exactly 22.4 liters (dm 3) at STP.STP = Standard Temperature and PressureTemp = 0ºC = 273KPressure = 1atm = 760 mmHg = 760 torr etc.This is often referred to as the “molar volume” of a gas.
Equal volumes of gases, at the same temperature and pressure, contain the same number of particles, or molecules.Thus, the number of molecules in a specific volume of gas is independent of the size or mass of the gas molecules.
Avogadro’s LawWhere “n” is the number of moles of gas presentMini Version: “At STP”
Problems Luis has 3.5 mol of H 2 gas at STP. What volume will this gas occupy?Joann has a balloon of CO2 gas that contains 0.180 mol CO2 at 1atm and 273K. If Joann let half of the gas out, what would the new volume be?
The Ideal Gas Law
Ideal Gas Law For a static situation (not a final and initial situation) you can relate the pressure, volume, moles, and temperature of a gasPV=nRTRearranging the equation gives us:P = (nRT)/VV = (nRT)/Pn = (PV)/(RT)T = (PV)/(nR)All temperatures must be in KELVIN!!!
The Universal Gas Constant R is the Universal Gas ConstantDepending on the units of pressure or volume, the R value will be differentR = 0.082 L x atm x K-1 x mol-1R = 62.36 L x torr x K-1 x mol-1R = 62.36 L x mmHg x K-1 x mol-1R = 8.315 L x kPa x K-1 x mol-1Make sure to match and cancel out the right units
Problems Rosy has a 5.0L tank of H 2 gas. If the pressure inside the tank is 800.0torr and the temperature is 300.0K, how many moles of hydrogen does her tank contain?Chris’ favorite meal is a bean and cheese burrito from Del Taco. Unfortunately, this means that his intestines were filled with 0.150 moles of CH4 gas under 2atm of pressure. What is the volume of gas that occupies his bowels? *Make an assumption about Temp*
Dalton ’s LawThe Law of Partial Pressures
John Dalton (1766-1844) English Chemist and PhysicistDid much research on color blindnessHe was colorblindFamous for his atomic theoryWorked with gases
Dalton’s Law: The total pressure exerted by a mixture of gases is the sum of the individual pressures of each gas in the mixtureDalton’s Equation:
ProblemsThe air in this room contains the gases shown below at their respective partial pressures in kPa. What is the pressure your body feels from the air in this room?
What is the pressure in problem 1 if you convert it to atm? Torr? mmHg? 3) Scuba Divers use gas mixtures of O2 and He. If the diver to your right breathes in a mixture that has a total pressure of 6.5 atm and a partial pressure from O2 of 1.2 atm, what is the partial pressure of He?
Liquids Particles close, but far apart enough to allow for movementSlide passed each otherFluidDefinite volumeNo definite shapeHigh densityLow compressibilityLow thermal expansion
Solids Atoms very closeDefinite shapeDefinite volumeHigh DensityVery small thermal expansion
Intermolecular forces Dispersion forcesDipole-dipoleHydrogen bondingIonic bonds
1) Dispersion forces Also called London forces or van der Waals forcesCaused by momentary dipoles in atoms or otherwise non-polar moleculesEffect is often seen in very large molecules
2) Dipole-Dipole Attractions Attraction between two polar molecules Positive end of one molecule is attracted to the negative end of another molecule
3) Hydrogen bonding Special dipole-dipole attraction Occurs between the H that is bonded to a very electronegative atom (O, N, F) on one molecule and the lone pair(s) on a very electronegative atom on another moleculeSurface tension
4) Ionic bonds Occur between ions Usually a metal and a non-metal Hold ions close togetherRequire large amounts of energy to breakExample: M.P. of NaCl = 801°C
Interaction Relative Strength Ionic 1000 Hydrogen Bond 100 Dipole-Dipole 10 Dispersion 1
Practice Identify the major intermolecular force for the following moleculesCl2NH3C10H22 KIHBr
a.k.a. freezing Change of State
Substance M.P. (°C) B.P. (°C) H2O0100 Au 1064 2856 CH 4 -182.5 -161.6 NaCl 801 1465
Chapter 7 checklistNature of gasesPressureBoyles, Charles, Gay-Lussacs, Combined, Avogadros, Ideal gas laws.STP- standard temperature and pressure, 273 K, 1 atm, 1 mole gas = 22.4LDaltons lawIntermolecular Forces – ionic bonds, dipol-dipole, hydrogen-bonding, london dispersionKnow relative strengths!!