chemistry of the air knockhardy publishing 2008 specifications
TRANSCRIPT
CHEMISTRYCHEMISTRY
OF THE AIROF THE AIR
KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING2008 2008
SPECIFICATIONSSPECIFICATIONS
INTRODUCTION
This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.
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www.knockhardy.org.uk/sci.htm
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KNOCKHARDY PUBLISHINGKNOCKHARDY PUBLISHING
CHEMISTRY OF THE AIRCHEMISTRY OF THE AIR
CONTENTS• Greenhouse gases
• Greenhouse effect
• Ozone layer
• Pollutants
• Catalytic converters
CHEMISTRY OF THE AIRCHEMISTRY OF THE AIR
GREENHOUSE GASESGREENHOUSE GASES
CARBON DIOXIDE CO2 contains C = O bonds
WATER VAPOUR H2O contains O - H bonds
METHANE CH4 contains C - H bonds
The ‘Greenhouse Effect’ of a given gas is dependent on its...
• atmospheric concentration
• ability to absorb infrared radiation
GREENHOUSE GASESGREENHOUSE GASES
Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.
GREENHOUSE GASESGREENHOUSE GASES
Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.
Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.
GREENHOUSE GASESGREENHOUSE GASES
Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.
Various types of vibration are possible. Bending and stretching are two examples and are found in water molecules. Each occurs at a different frequency.
Symmetric Bending Asymmetricstretching stretching
GREENHOUSE GASESGREENHOUSE GASES
Different covalent bonds have different strengths due to the masses of different atoms at either end of the bond. As a result, they vibrate at different frequencies (imagine two balls on either end of a spring) . The frequency of vibration can be found by detecting when the molecules absorb electro-magnetic radiation.
Various types of vibration are possible. Carbon dioxide also undergoes bending and stretching.
Bending in a carbon dioxide molecule
GREENHOUSE GASESGREENHOUSE GASES
The frequencies lie in the INFRA REDINFRA RED part of the electromagnetic spectrum and can be detected using infra red spectroscopy.
An infra red spectrum of atmospheric air
It is the absorption of infra red radiation by atmospheric gases such as methane, carbon dioxide and water vapour that contributes to global warming.
H2O
H2OCO2
CO2
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
47% reaches the earth
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
radiation re-emitted from the earth is in the infra red region
47% reaches the earth
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
radiation re-emitted from the earth is in the infra red region
70% of the radiation returns to space
47% reaches the earth
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
radiation re-emitted from the earth is in the infra red region
70% of the radiation returns to space
47% reaches the earth
greenhouse gasesabsorb the remainder
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
radiation re-emitted from the earth is in the infra red region
70% of the radiation returns to space
47% reaches the earth
greenhouse gasesabsorb the remainder
energy is returned to earth to keep it warm
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
energy from the sun is in the ultra violet, visible and infra red regions
radiation re-emitted from the earth is in the infra red region
70% of the radiation returns to space
greenhouse gasesabsorb the remainder
47% reaches the earth
energy is returned to earth to keep it warm
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
SummarySummary
• energy from the sun is in the ultra violet, visible and infra red regions
• the earth is warmed up by the energy
• radiation re-emitted from the earth is in the infra red region
• 70% of the radiation (between 7000nm and 12500nm) returns to space
• greenhouse gases absorb the remainder
Gas wavelength of radiation adsorbed / nmCO2 12500 - 17000H2O 4500 - 7000 and above 17000
• they can return this energy to earth to keep it warm
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
ProblemsAn increase in the concentration of greenhouse gases leads to climate change / global warming.
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
ProblemsAn increase in the concentration of greenhouse gases leads to climate change / global warming.
PossibleEffects
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
ProblemsAn increase in the concentration of greenhouse gases leads to climate change / global warming.
PossibleEffects • higher temperatures
• melting ice caps
• rise in sea levels
• flooding of low-lying lands
• changes in crop patterns
• deserts move north
• change in food webs
• extinction of some species
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
What can chemists do to minimise climate change from global warming?
• provide scientific evidence to governments to confirm it is taking place
• monitor progress against initiatives such as the Kyoto protocol
• investigate solutions to environmental problems
THE GREENHOUSE EFFECTTHE GREENHOUSE EFFECT
What can chemists do to minimise climate change from global warming?
• provide scientific evidence to governments to confirm it is taking place
• monitor progress against initiatives such as the Kyoto protocol
• investigate solutions to environmental problems
plus
CARBON CAPTURE AND STORAGE (CCS)
• removal of waste carbon dioxide as a liquid injected deep in the oceans
• storage underground in deep geological formations
• reaction with metal oxides to form stable carbonate minerals.
MgO(g) + CO2(g) —> MgCO3(s)
or CaO(g) + CO2(g) —> CaCO3(s)
CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE
What is it?
• CO2 is collected from industrial processes and power generation
• it is separated and purified
• it is then transported to a suitable long-term storage site
CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE
What is it?
• CO2 is collected from industrial processes and power generation
• it is separated and purified
• it is then transported to a suitable long-term storage site
Storage possibilities
• gaseous storage in deep geological formations
• liquid storage in the ocean
• solid storage by reaction as stable carbonates
CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE
What is it?
• CO2 is collected from industrial processes and power generation
• it is separated and purified
• it is then transported to a suitable long-term storage site
Storage possibilities
• gaseous storage in deep geological formations
• liquid storage in the ocean
• solid storage by reaction as stable carbonates
How can it help?
• could reduce CO2 emissions from power stations by 80%
• could be used to store CO2 emitted from fermentation processes
CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE
What is it?
• CO2 is collected from industrial processes and power generation
• it is separated and purified
• it is then transported to a suitable long-term storage site
Storage possibilities
• gaseous storage in deep geological formations
• liquid storage in the ocean
• solid storage by reaction as stable carbonates
How can it help?
• could reduce CO2 emissions from power stations by 80%
• could be used to store CO2 emitted from fermentation processes
CCARBON DOXIDE ARBON DOXIDE CCAPTURE & APTURE & SSTORAGETORAGE
CO2 in geological structures is actually a naturally occurring phenomenon
• CO2 is pumped deep underground
• it is compressed by the higher pressures
• it becomes a liquid, which is trapped between the grains of rock
• impermeable rock prevents the CO2 rising back to the surface • drilling for CO2 can be used for enhanced oil or gas recovery
Over time CO2 can react with the minerals in the rock, forming new minerals and providing increased storage security.
DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER
Although ozone is a reactive and poisonous gas, it protects us from harmful UV radiation which would affect life on earth. UV radiation can cause skin cancer.
DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER
Although ozone is a reactive and poisonous gas, it protects us from harmful UV radiation which would affect life on earth. UV radiation can cause skin cancer.
Ozone in the stratosphere 2O3 —> 3O2
breaks down naturally
Ozone (trioxygen) can break up O3 —> O• + O2
to give ordinary oxygen and anoxygen radical
DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER
Although ozone is a reactive and poisonous gas, it protects us from harmful UV radiation which would affect life on earth. UV radiation can cause skin cancer.
Ozone in the stratosphere 2O3 —> 3O2
breaks down naturally
Ozone (trioxygen) can break up O3 —> O• + O2
to give ordinary oxygen and anoxygen radical
Ultra violet light can supply the energy for the process. That is why the ozone layer is important as it protects us from the harmful rays.
BUTbreakdown is easier in the presence of chlorofluorocarbons (CFC's)
DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER
EFFECT OF CFC’SEFFECT OF CFC’S
There is a series of complex reactions but the basic process is :-
CFC's break down in the presence CCl2F2 —> Cl• + CClF2
of UV light to form chlorine radicals
chlorine radicals react with ozone O3 + Cl• —> ClO• + O2
chlorine radicals are regenerated ClO• + O —> O2 + Cl•
Overall chlorine radicals are not used up so a small amount of CFC's can destroy thousands of ozone molecules before the termination stage.
DEPLETION OF THE OZONE LAYERDEPLETION OF THE OZONE LAYER
OXIDES OF NITROGEN NOxOXIDES OF NITROGEN NOx
Oxides of nitrogen, NOx, formed during thunderstorms or by aircraft break down to give NO (nitrogen monoxide) which also catalyses the breakdown of ozone.
nitrogen monoxide reacts with ozone O3 + NO —> NO2 + O2
nitrogen monoxide is regenerated NO2 + O —> O2 + NO
POLLUTANTSPOLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINESPOLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Carbon monoxide CO
Origin • incomplete combustion of hydrocarbons in petrolbecause not enough oxygen was present
Effect • poisonous • combines with haemoglobin in blood • prevents oxygen being carried to cells
Process C8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)
POLLUTANTSPOLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINESPOLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Oxides of nitrogen NOx - NO, N2O and NO2
Origin • combination of atmospheric nitrogen andoxygen under high temperature
Effect • aids formation of photochemical smog which is irritating to eyes, nose, throat
• aids formation of low level ozone which affects plants and is irritating to eyes, nose and throat
Process sunlight breaks oxides NO2 —> NO + Oozone is produced O + O2 —> O3
POLLUTANTSPOLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINESPOLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Unburnt hydrocarbons CxHy
Origin • hydrocarbons that have not undergone combustion
Effect • toxic and carcinogenic (cause cancer)
POLLUTANTSPOLLUTANTS
POLLUTANT FORMATIONPOLLUTANT FORMATION
Nitrogen combines with oxygenN2(g) + O2(g) —> 2NO(g)
Nitrogen monoxide is oxidised2NO(g) + O2(g) —> 2NO2(g)
Incomplete hydrocarbon combustionC8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)
POLLUTANTSPOLLUTANTS
POLLUTANT REMOVALPOLLUTANT REMOVAL
Oxidation of carbon monoxide2CO(g) + O2(g) —> 2CO2(g)
Removal of NO and CO2CO(g) + 2NO(g) —> N2(g) + 2CO2(g)
Aiding complete hydrocarbon combustionC8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
REMOVAL OF NOx and COREMOVAL OF NOx and CO
• CO is converted to CO2
• NOx are converted to N2
2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
REMOVAL OF NOx and COREMOVAL OF NOx and CO
• CO is converted to CO2
• NOx are converted to N2
2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)
• Unburnt hydrocarbons converted to CO2 and H2O
C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
REMOVAL OF NOx and COREMOVAL OF NOx and CO
• CO is converted to CO2
• NOx are converted to N2
2NO(g) + 2CO(g) —> N2(g) + 2CO2(g)
• Unburnt hydrocarbons converted to CO2 and H2O
C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)
• catalysts are rare metals - RHODIUM, PALLADIUM
• metals are finely divided for a greater surface area - this provides more active sites
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
STAGES OF OPERATIONSTAGES OF OPERATION
Adsorption • NO and CO seek out active sites on the surface• they bond with surface
• weakens the bonds in the gas molecules
• makes a subsequent reaction easier
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
STAGES OF OPERATIONSTAGES OF OPERATION
Reaction • being held on the surface increases chance of favourable collisions
• bonds break and re-arrange
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
STAGES OF OPERATIONSTAGES OF OPERATION
Desorption • products are released from the active sites
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
STAGES OF OPERATIONSTAGES OF OPERATION
Adsorption Reaction Desorption
CATALYTIC CONVERTERSCATALYTIC CONVERTERS
STAGES OF OPERATIONSTAGES OF OPERATION
Adsorption • NO and CO seek out active sites on the surface• they bond with surface
• weakens the bonds in the gas molecules
• makes a subsequent reaction easier
Reaction • being held on the surface increases chance of favourable collisions
• bonds break and re-arrange
Desorption • products are released from the active sites