the air around us air is more than one removed from nothing
TRANSCRIPT
The Air Around UsThe Air Around Us
Air is more than one Air is more than one removed from nothingremoved from nothing
Learning objectivesLearning objectives
Describe what is meant by pressure Describe what is meant by pressure Identify units of gas pressureIdentify units of gas pressure Describe the basic gas lawsDescribe the basic gas laws Apply gas laws to simple problemsApply gas laws to simple problems Describe composition of the atmosphereDescribe composition of the atmosphere Name important pollutants and their effectsName important pollutants and their effects Describe origin of the ozone holeDescribe origin of the ozone hole
Gas laws and crash safetyGas laws and crash safety
The airbag is chemistry applied in a very The airbag is chemistry applied in a very practical areapractical area
Airbags have reduced serious injuries and Airbags have reduced serious injuries and fatalities by significant marginfatalities by significant margin
Chemistry plays a crucial role in airbag Chemistry plays a crucial role in airbag performanceperformance
Timing is everythingTiming is everything
The airbag must deploy within about 40 ms The airbag must deploy within about 40 ms of the impactof the impact
The airbag must not deploy unless there is The airbag must not deploy unless there is an impactan impact
Inflation depends upon a rapid chemical Inflation depends upon a rapid chemical reaction generating a quantity of gasreaction generating a quantity of gas
The bag, once inflated, must then deflate at The bag, once inflated, must then deflate at the point of impact with the driver to prevent the point of impact with the driver to prevent injuryinjury
Gas: no interactionsGas: no interactions
Not rigidNot rigid Completely fills containerCompletely fills container CompressibleCompressible Low densityLow density
Atom motion and temperatureAtom motion and temperature
Atoms in molecules have three types of Atoms in molecules have three types of motionmotion Rotation – moving about the centre of massRotation – moving about the centre of mass Vibration – vibrating about the centre of massVibration – vibrating about the centre of mass Translation – movement of the centre of massTranslation – movement of the centre of mass
As temperature increases, the energies of As temperature increases, the energies of all types of motion increaseall types of motion increase
In gases molecular energies exceeds all In gases molecular energies exceeds all interactionsinteractions
Kinetic molecular theory and Kinetic molecular theory and pressure – a case for atomspressure – a case for atoms
Pressure is caused by the energetic Pressure is caused by the energetic molecules striking the tire wallmolecules striking the tire wall
Pumping up a tire increases the number of Pumping up a tire increases the number of moleculesmolecules
More molecules – higher pressureMore molecules – higher pressure Higher temperature – higher pressureHigher temperature – higher pressure
Under pressureUnder pressure
Gases exert pressure by virtue of motionGases exert pressure by virtue of motion Gravity makes the air density higher near Gravity makes the air density higher near
the earth’s surfacethe earth’s surface Pressure decreases with elevationPressure decreases with elevation
Atmospheric pressureAtmospheric pressure
BarometerBarometer is used for measuring is used for measuring atmospheric pressureatmospheric pressure
Atmospheric pressureAtmospheric pressure
The weight of the air supports a column of The weight of the air supports a column of mercury 760 mm highmercury 760 mm high
Nominally atmospheric pressure is 760 mm Nominally atmospheric pressure is 760 mm HgHg
Atmospheric pressure changes with the Atmospheric pressure changes with the weatherweather
Units of pressureUnits of pressure
Gas laws: experience in math formGas laws: experience in math form
The properties of gases can be described by a The properties of gases can be described by a number of simple lawsnumber of simple laws
The laws establish quantitative relationships The laws establish quantitative relationships between different variablesbetween different variables
They are largely intuitively obvious and familiarThey are largely intuitively obvious and familiar
The four variablesThe four variables
Pressure (P)Pressure (P) Volume (V)Volume (V) Temperature (T in Kelvin)Temperature (T in Kelvin) Number of molecules (n in moles)Number of molecules (n in moles)
Variables and constantsVariables and constants
In the elementary gas laws two of the four In the elementary gas laws two of the four variables are kept constantvariables are kept constant
Each law describes how one variable reacts Each law describes how one variable reacts to changes in another variableto changes in another variable
All the simple laws can be integrated into All the simple laws can be integrated into one combined gas lawone combined gas law
Boyle’s lawBoyle’s law
The first experimental gas lawThe first experimental gas law Pressure increases, volume decreases (T, n Pressure increases, volume decreases (T, n
constant)constant)1
PV
Charles’ LawCharles’ Law
As temperature increases, volume As temperature increases, volume increases (P, n constant)increases (P, n constant) Temperature must be measured in KelvinTemperature must be measured in Kelvin
V T
Absolute zeroAbsolute zero
Gay-Lussac observed V changed by 1/273 Gay-Lussac observed V changed by 1/273 of value at 0of value at 0ºCºC
Plotted as V = Plotted as V = kkT (T = ºC + 273):T (T = ºC + 273): V = 0 at T = 0 KV = 0 at T = 0 K
Does the gas actually occupy zero volume?Does the gas actually occupy zero volume? No, at lower T the law is not followedNo, at lower T the law is not followed
Combined gas lawCombined gas law
Fold together Boyle and Charles:Fold together Boyle and Charles: PP11VV11/T/T11 = P = P22VV22/T/T22
Given five of the variables, find the sixthGiven five of the variables, find the sixth Units must be consistentUnits must be consistent Temperature in KelvinTemperature in Kelvin
Standard temperature and pressure Standard temperature and pressure (STP)(STP)
Standard conditions allow direct comparison Standard conditions allow direct comparison of properties of different substancesof properties of different substances Standard temperature is 273 K (0Standard temperature is 273 K (0ºC)ºC) Standard pressure is 760 mm Hg or 1 Standard pressure is 760 mm Hg or 1
atmosphereatmosphere
At STP, 1 mole of At STP, 1 mole of anyany ideal gas occupies ideal gas occupies 22.414 L22.414 L
What is the atmosphereWhat is the atmosphere
The atmosphere is layeredThe atmosphere is layered
TroposphereTroposphere Where the weather happensWhere the weather happens
StratosphereStratosphere Where the ozone isWhere the ozone is
MesosphereMesosphere IonosphereIonosphere
The brutal strength of solar radiation ionizes all the The brutal strength of solar radiation ionizes all the components – permits transmission of radio signals components – permits transmission of radio signals around the earth without need of mirrorsaround the earth without need of mirrors
Pollutants: things that shouldn’t be Pollutants: things that shouldn’t be therethere
SOSO22 power plant emissionspower plant emissions PM-10 PM-10 particulate matter from agriculture and particulate matter from agriculture and
constructionconstruction CO CO vehicle emissionsvehicle emissions OO33 sunlight and vehicle emissionssunlight and vehicle emissions NONO22 vehicle emissionsvehicle emissions Pb Pb smelters and battery plantssmelters and battery plants
Cleaning up our act: successesCleaning up our act: successes
Clean Air Act of 1970Clean Air Act of 1970 Amended in 1977Amended in 1977 Top six pollutants have all decreasedTop six pollutants have all decreased Problems remainProblems remain
Ozone: still a problemOzone: still a problem
Bad ozone, good ozoneBad ozone, good ozone
Stratospheric sunscreenStratospheric sunscreen OO33 + UV = O + UV = O22 + O + O
OO22 + O = O + O = O33 + heat + heat
Chlorofluorocarbons (CFCs): wonder chemicalsChlorofluorocarbons (CFCs): wonder chemicals
ApplicationsApplications PropertiesProperties
RefrigerationRefrigeration ColorlessColorless
Air-conditioningAir-conditioning NontoxicNontoxic
PropellantsPropellants InertInert
Foaming agentsFoaming agents OdorlessOdorless
Hidden dangersHidden dangers
CFCs are unstable in UVCFCs are unstable in UVCFCF22ClCl22 + UV = Cl + CF + UV = Cl + CF22ClCl
Cl radicals catalyze decomposition of ozoneCl radicals catalyze decomposition of ozoneCl + OCl + O33 = ClO = ClO + O+ O22
OO33 + UV = O + UV = O22 + O + O
ClO + O = Cl + OClO + O = Cl + O22
One Cl atom can react again and again destroying One Cl atom can react again and again destroying countless Ocountless O33 molecules molecules
The Antarctic ozone holeThe Antarctic ozone hole
Ozone depletion in the Antarctic is severeOzone depletion in the Antarctic is severe Stratosphere isolated by polar vortexStratosphere isolated by polar vortex Polar stratospheric clouds (PSCs) formPolar stratospheric clouds (PSCs) form Clouds produce chlorine gasClouds produce chlorine gas
Montreal Protocol and CFCsMontreal Protocol and CFCs
Phase-out of CFCs began 1978Phase-out of CFCs began 1978 Montreal Protocol (1987) called for 50 % decrease Montreal Protocol (1987) called for 50 % decrease
by 2000 by 2000 Amended to complete phaseoutAmended to complete phaseout Chemical ingenuity required for alternatives like Chemical ingenuity required for alternatives like
HCFCsHCFCs