CHEMISTRY OF THE AIR KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS

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. Individual students may use the material at home for revision purposes or it may be used for classroom teaching with an interactive white board. Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at... Navigation is achieved by... either clicking on the grey arrows at the foot of each page orusing the left and right arrow keys on the keyboard KNOCKHARDY PUBLISHING CHEMISTRY OF THE AIR

CONTENTS Greenhouse gases Greenhouse effect Ozone layer Pollutants Catalytic converters CHEMISTRY OF THE AIR

GREENHOUSE GASES CARBON DIOXIDECO 2 containsC = O bonds WATER VAPOURH 2 OcontainsO - H bonds METHANECH 4 containsC - H bonds The ‘Greenhouse Effect’ of a given gas is dependent on its... atmospheric concentration ability to absorb infrared radiation

GREENHOUSE 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 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 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 Asymmetric stretching

GREENHOUSE 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 GASES INFRA RED The frequencies lie in the INFRA 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. H2OH2O H2OH2O CO 2

THE GREENHOUSE EFFECT energy from the sun is in the ultra violet, visible and infra red regions

THE GREENHOUSE EFFECT energy from the sun is in the ultra violet, visible and infra red regions 47% reaches the earth

THE 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 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 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 gases absorb the remainder

THE 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 gases absorb the remainder energy is returned to earth to keep it warm

THE 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 gases absorb the remainder 47% reaches the earth energy is returned to earth to keep it warm

THE GREENHOUSE EFFECT Summary 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 / nm CO H 2 O and above they can return this energy to earth to keep it warm

THE GREENHOUSE EFFECT Problems An increase in the concentration of greenhouse gases leads to climate change / global warming.

THE GREENHOUSE EFFECT Problems An increase in the concentration of greenhouse gases leads to climate change / global warming. Possible Effects

THE GREENHOUSE EFFECT Problems An increase in the concentration of greenhouse gases leads to climate change / global warming. Possible Effects 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 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 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) + CO 2 (g) —> MgCO 3 (s) or CaO(g) + CO 2 (g) —> CaCO 3 (s)

CARBON DOXIDE CAPTURE & STORAGE

What is it? CO 2 is collected from industrial processes and power generation it is separated and purified it is then transported to a suitable long-term storage site

CARBON DOXIDE CAPTURE & STORAGE What is it? CO 2 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

CARBON DOXIDE CAPTURE & STORAGE What is it? CO 2 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 CO 2 emissions from power stations by 80% could be used to store CO 2 emitted from fermentation processes

CARBON DOXIDE CAPTURE & STORAGE What is it? CO 2 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 CO 2 emissions from power stations by 80% could be used to store CO 2 emitted from fermentation processes

CARBON DOXIDE CAPTURE & STORAGE CO 2 in geological structures is actually a naturally occurring phenomenon CO 2 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 CO 2 rising back to the surface drilling for CO 2 can be used for enhanced oil or gas recovery Over time CO 2 can react with the minerals in the rock, forming new minerals and providing increased storage security.

DEPLETION 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 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 stratosphere2O 3 —> 3O 2 breaks down naturally Ozone (trioxygen) can break upO 3 —> O + O 2 to give ordinary oxygen and an oxygen radical

DEPLETION 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 stratosphere2O 3 —> 3O 2 breaks down naturally Ozone (trioxygen) can break upO 3 —> O + O 2 to give ordinary oxygen and an oxygen 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. BUT breakdown is easier in the presence of chlorofluorocarbons (CFC's)

DEPLETION OF THE OZONE LAYER EFFECT OF CFC’S There is a series of complex reactions but the basic process is :- CFC's break down in the presenceCC l 2 F 2 —> C l + CC l F 2 of UV light to form chlorine radicals chlorine radicals react with ozone O 3 + C l —> C l O + O 2 chlorine radicals are regeneratedC l O + O —> O 2 + C l Overallchlorine 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 LAYER OXIDES 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 O 3 + NO —> NO 2 + O 2 nitrogen monoxide is regenerated NO 2 + O —> O 2 + NO

POLLUTANTS POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES Carbon monoxide CO Origin incomplete combustion of hydrocarbons in petrol because not enough oxygen was present Effect poisonous combines with haemoglobin in blood prevents oxygen being carried to cells ProcessC 8 H 18 (g) + 8½O 2 (g) —> 8CO(g) + 9H 2 O(l)

POLLUTANTS POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES Oxides of nitrogen NOx - NO, N 2 O and NO 2 Origin combination of atmospheric nitrogen and oxygen 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 Processsunlight breaks oxidesNO 2 —> NO + O ozone is produced O + O 2 —> O 3

POLLUTANTS POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES Unburnt hydrocarbons C x H y Origin hydrocarbons that have not undergone combustion Effect toxic and carcinogenic (cause cancer)

POLLUTANTS POLLUTANT FORMATION Nitrogen combines with oxygen N 2 (g) + O 2 (g) —> 2NO(g) Nitrogen monoxide is oxidised 2NO(g) + O 2 (g) —> 2NO 2 (g) Incomplete hydrocarbon combustion C 8 H 18 (g) + 8½O 2 (g) —> 8CO(g) + 9H 2 O(l)

POLLUTANTS POLLUTANT REMOVAL Oxidation of carbon monoxide 2CO(g) + O 2 (g) —> 2CO 2 (g) Removal of NO and CO 2CO(g) + 2NO(g) —> N 2 (g) + 2CO 2 (g) Aiding complete hydrocarbon combustion C 8 H 18 (g) + 12½O 2 (g) —> 8CO 2 (g) + 9H 2 O(l)

CATALYTIC CONVERTERS REMOVAL OF NOx and CO CO is converted to CO 2 NOx are converted to N 2 2NO(g) + 2CO(g) —> N 2 (g) + 2CO 2 (g)

CATALYTIC CONVERTERS REMOVAL OF NOx and CO CO is converted to CO 2 NOx are converted to N 2 2NO(g) + 2CO(g) —> N 2 (g) + 2CO 2 (g) Unburnt hydrocarbons converted to CO 2 and H 2 O C 8 H 18 (g) + 12½O 2 (g) —> 8CO 2 (g) + 9H 2 O(l)

CATALYTIC CONVERTERS REMOVAL OF NOx and CO CO is converted to CO 2 NOx are converted to N 2 2NO(g) + 2CO(g) —> N 2 (g) + 2CO 2 (g) Unburnt hydrocarbons converted to CO 2 and H 2 O C 8 H 18 (g) + 12½O 2 (g) —> 8CO 2 (g) + 9H 2 O(l) catalysts are rare metals - RHODIUM, PALLADIUM metals are finely divided for a greater surface area - this provides more active sites

CATALYTIC CONVERTERS STAGES OF OPERATION

CATALYTIC CONVERTERS STAGES 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 CONVERTERS STAGES OF OPERATION Reaction being held on the surface increases chance of favourable collisions bonds break and re-arrange

CATALYTIC CONVERTERS STAGES OF OPERATION Desorption products are released from the active sites

CATALYTIC CONVERTERS STAGES OF OPERATION Adsorption Reaction Desorption

CATALYTIC CONVERTERS STAGES 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

©2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING THE END CHEMISTRY OF THE AIR