Transcript No Slide Title

CHEMISTRY
OF THE AIR
KNOCKHARDY PUBLISHING
2008
SPECIFICATIONS
KNOCKHARDY PUBLISHING
CHEMISTRY OF THE AIR
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...
www.knockhardy.org.uk/sci.htm
Navigation is achieved by...
either
clicking on the grey arrows at the foot of each page
or
using the left and right arrow keys on the keyboard
CHEMISTRY OF THE AIR
CONTENTS
• Greenhouse gases
• Greenhouse effect
• Ozone layer
• Pollutants
• Catalytic converters
GREENHOUSE GASES
CARBON DIOXIDE
CO2
contains
C = O bonds
WATER VAPOUR
H 2O
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 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
stretching
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
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
H2O
CO2
CO2
H2O
It is the absorption of infra red radiation by atmospheric gases such
as methane, carbon dioxide and water vapour that contributes to
global warming.
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
47% reaches the earth
radiation re-emitted from the
earth is in the infra red region
THE GREENHOUSE EFFECT
energy from the sun is in the
ultra violet, visible and infra
red regions
47% reaches the earth
radiation re-emitted from the
earth is in the infra red region
70% of the radiation
returns to space
THE GREENHOUSE EFFECT
energy from the sun is in the
ultra violet, visible and infra
red regions
47% reaches the earth
radiation re-emitted from the
earth is in the infra red region
70% of the radiation
returns to space
greenhouse gases
absorb the remainder
THE GREENHOUSE EFFECT
energy from the sun is in the
ultra violet, visible and infra
red regions
47% reaches the earth
radiation re-emitted from the
earth is in the infra red region
70% of the radiation
returns to space
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
47% reaches the earth
radiation re-emitted from the
earth is in the infra red region
70% of the radiation
returns to space
greenhouse gases
absorb the remainder
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
CO2
H2O
wavelength of radiation adsorbed / nm
12500 - 17000
4500 - 7000 and above 17000
• 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.
or
MgO(g) + CO2(g) —> MgCO3(s)
CaO(g) + CO2(g) —> CaCO3(s)
CARBON DOXIDE CAPTURE & STORAGE
CARBON DOXIDE CAPTURE & STORAGE
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
CARBON DOXIDE CAPTURE & STORAGE
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
CARBON DOXIDE CAPTURE & STORAGE
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
CARBON DOXIDE CAPTURE & STORAGE
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
CARBON DOXIDE CAPTURE & STORAGE
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 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 stratosphere
breaks down naturally
2O3
Ozone (trioxygen) can break up
to give ordinary oxygen and an
oxygen radical
O3
—>
—>
3O2
O•
+
O2
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 stratosphere
breaks down naturally
2O3
Ozone (trioxygen) can break up
to give ordinary oxygen and an
oxygen radical
O3
—>
—>
3O2
O•
+
O2
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 presence
of UV light to form chlorine radicals
CCl2F2 —> Cl•
chlorine radicals react with ozone
O3 + Cl• —> ClO• + O2
chlorine radicals are regenerated
ClO• + O —> O2 + Cl•
Overall
+ CClF2
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 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
O3 + NO —> NO2 + O2
nitrogen monoxide is regenerated
NO2 + O —> O2
+ 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
Process
C8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)
POLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Oxides of nitrogen NOx - NO, N2O and NO2
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
Process
sunlight breaks oxides
ozone is produced
NO2 —> NO + O
O + O2 —> O3
POLLUTANTS
POLLUTANT GASES FROM INTERNAL COMBUSTION ENGINES
Unburnt hydrocarbons CxHy
Origin
• hydrocarbons that have not undergone combustion
Effect
• toxic and carcinogenic (cause cancer)
POLLUTANTS
POLLUTANT FORMATION
Nitrogen combines with oxygen
N2(g) + O2(g) —> 2NO(g)
Nitrogen monoxide is oxidised
2NO(g) + O2(g) —> 2NO2(g)
Incomplete hydrocarbon combustion
C8H18(g) + 8½O2(g) —> 8CO(g) + 9H2O(l)
POLLUTANTS
POLLUTANT REMOVAL
Oxidation of carbon monoxide
2CO(g) + O2(g) —> 2CO2(g)
Removal of NO and CO
2CO(g) + 2NO(g) —> N2(g) + 2CO2(g)
Aiding complete hydrocarbon combustion
C8H18(g) + 12½O2(g) —> 8CO2(g) + 9H2O(l)
CATALYTIC CONVERTERS
REMOVAL OF NOx and CO
• CO is converted to CO2
• NOx are converted to N2
2NO(g)
+
2CO(g)
—>
N2(g)
+
2CO2(g)
CATALYTIC CONVERTERS
REMOVAL 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 CONVERTERS
REMOVAL 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 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
CHEMISTRY
OF THE AIR
THE END
©2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING