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Chapter 10

Chapter 10: Gases

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CEM 151

Chapter 10 GasesTuesday June 24 20141214 PMCharacteristics of GasesPressure of a GasComposed of nonmetallic elements usually mercury is an exceptionPressure is the amount of force that acts on a given areaOnly few elements exist as gases under ordinary conditions of temperaturePFANoble gases are monoatomicDepends on several factorsHNO and Clare diatomic gasesNumber of gas particles in a given volume2222Many low molar mass molecular compounds are gasesVolume of the containerOften referred to as vaporsAverage speed of the gas particlesHave no filled shape or volumeMeasured by barometers manometers and other devicesMercury BarometerExpands spontaneously to fill its container and equals the volume and the The pressure of the atmosphere on the surface of the mercury equals the shape of the containerpressure of the column of mercuryAlways form homogeneous mixtures with other gasesWhen the atmospheric pressure decreases the mercury level in a Are highly compressible and expand to fill their containersbarometer will decreaseThe individual molecules are relatively far apartThe actual atmospheric pressure at a specific location depends on the In air the molecules take up about 01 of the total volume the rest is altitude and weather conditionsempty spaceManometerHave extremely low densitiesA manometer is used to measure the pressure of an enclosed gas Their Particles are constantly moving and colliding especially with container wallsoperation is similar to the barometer and they usually contain mercuryCollisions of particles with surfaces result in pressureStandard PressureMathematical relationship for the study of gasesNormal atmospheric pressure at sea level is referred to as standard pressureThere are four physical quantities measured in the study of gasesIt is equal toPressure Volume Temperature and quantity moles100 atmBoyles Law relates Pressure to Volume760 torr 760 mmHgCharless Law relates Volume to temperatureAvogadros Law relates Volume toof moles101kPaThe Ideal Gas Law relates al quantities togetherSTP and Molar VolumeBoyles LawStandard Temperature and Pressure STPRobert Boyle 16271691 studied the relationship between the pressure exerted oP1000 atmosphere and T0C27315 Kon a gas and the resulting volume of the gas1 mole of any gas2241 L at STPThe volume of a fixed quantity of gas at constant T is inversely proportional to 2241 L is called Molar Volumeof a gassthe pressurePVTConstantGas DensityPVK TConstantIdeal gas law is used to calculate the density and molar mass of a gasNew volume of gas when pressure is changed at constant temperature can be Mass in grams of gasgcalculated using the equationMolar mass of gasPVPVTconstant1122NgCharless LawDgVJacques Charles 17461823nVPRTThe volume of gas is directly proportional to the absolute temperature KelvingVPRTVTd PRTVTk PConstantDPRTKa proportionality constantDaltons Law of Partial PressuresVTVT1122How do we deal with gases composed of a mixture of two or more different Avogadros LawgasesAvogadros hypothesis equal volumes of gases at the same temperature and John Dalton 17661844 The total pressure of the mixture of gases equals the pressure contain the same number of moleculessum of the partial pressures of all the gasesAvogadros Law for a gas at constant temperature and pressure the volume is P P P P total123directly proportional to the number of moles of gasPartial Pressure the pressure of each gas would exert if it were the only gas in Vnthe containerVknMole Fraction and Partial PressureKproportionality constantMole Fraction the ratio of the number of moles of a given component in a VnVn1122mixture to the total number of moles in the mixtureIdealGas EquationX nnThree historically important gas laws derived relationships between two physical 11totalMole fraction of each component in a mixture of ideal gases is directly properties of gas while keeping other properties constantproportional to its partial pressurePVnRTP x PPpressure in atm11totalVvolume in LVolume of Gases in Chemical ReactionsNmolesThe principles of reaction stoichiometry from chapter 4 can be combined with the Rproportionality constant11gas laws for reactions involving gases00821 L atm Kmolif P in atm11The volume of gas is given6236 L torr Kmolif P in mmHg or torrThe ideal gas law allows us to convert from the volume of the gas to moles Ttemp in kelvinof gas then we can use the coefficients in the equation as a mole ratio to Combined Gas Lawcalculate the grams of the required substanceCombining the Boyles Law and Charles Law gives an equation which relates the When gases are at STP use 1 mol224 Lthree variables PV and T for a gas sample at two sets of conditionsThe quantity of the gas n is kept constantThe amount of the reactant that produces gas is often given in gramsConvert grams to moles of the substance and use the coefficients in the PVT PVT111222equation as a mole ratio
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