atmospheric chemistry Flashcards
oxygen (the reactive gas)
- most reactive gas in air
- prep in lab by decomposition of hydrogen peroxide (H₂O₂)
- manufactured in industry by liquefaction followed by fractional distillation of air
- air turned into liquid + diff gases allowed to boil at diff temps
nitrogen (the unreactive gas)
- -most abundant gas in air (78%)
- colourless, odourless, tasteless gas
- so unreactive bc of large amount of energy required to break triple bond between N atoms
- essential for plant growth (need to make proteins)
- so unreactive it cannot be used directly by plants
nitrogen fixation
conversion of atmospheric nitrogen to useful compounds
two methods of nitrogen fixation
- during thunderstorms/lightning
- nitrogen-fixing bacteria
during thunderstorms
- discharge of electricity that takes place during thunderstorms provides enough energy for nitrogen + oxygen in air to react together.
- substance called nitrogen monoxide, NO, formed
- ntrogen monoxide reacts w/ oxygen from air to form nitrogen dioxide
- nitrogen dioxide dissolves in rainwater to form nitrous acid, HNO₃
nitrogen-fixing bacteria
- plants called legumes (eg. peas, beans) have tiny root swellings containing rhizobium bacteria which can fix nitrogen
- not enough nitrogen fixed by natural processes to provide for out needs
- soils for growing crops must have fertiliser added
- fertiliser produced by artificial fixation (eg. Haber process)
nitrogen recycling
- nitrogen must be recycled throughout an ecosystem + returned to atmosphere
- bacteria called nitrifying + denitrifying bacteria necessary in process of recyling
- nitrogen cycle
inorganic carbon compounds
- carbon dioxide,
- carbon monoxide (CO),
- carbonate compounds,
- hydrogencarbonate compounds,
- carbides
carbon burned in limited supply of oxygen
- if carbon burned in limited supply of oxygen, carbon monoxide formed instead of carbon diozide
eg. in car engines, in cigarette smoke
the carbon cycle
- percentage of carbon dioxide in atmosphere fairly constant at 0.03%
- some processes remove CO₂ from air, others return it to air
processes that remove CO₂ from air
-photosynthesis
6CO₂ + 6H₂O –> C₆H₁₂O₆ + 6O₂
-dissolving in rainwater, rivers, oceans, some of the CO₂ becomes incorporated into limestone
processes that return CO₂ to the air
- respiration by living things
- burning of fossil fuels
- roasting of limestone
the green house effect
Greenhouse gases: CO₂, water vapour
-greenhouse effect keeps the earth warm enough to live on
greenhouse factor
measure of the greenhouse effect (heat-absorbing properties) of a particular gas when compared with carbon dioxide
what gases are not greenhouse gases?
nitrogen
oxygen
increase in greenhouse gases - carbon diozide
- human activities leading to inc in conc of greenhouse gases in air
- level of CO₂ giving cause for concern. Burning of of fossil fuels results in large amounts of CO₂ being added to air
- inc in rate at which CO₂ released into air not matched by rate at which it is removed by photosynthesis or by dissolving in oceans etc
- residence time of CO₂in air about 100 years
greenhouse gases
methane
CFCs (chlorofluorocarbons)
dinitrogen oxide N₂O
methane - activity that is increasing its concentration
- increasing size of cattle herds - animals release large amount of methane from intestines
- growing of rice in paddy fields
- anaerobic breakdown of organic material in rubbish dumps
methane - residence time
10 years
CFCs (chlorofluorocarbons) - activity that is increasing its concentration
- propellant gas in aerosol sprays
- discarded fridges
CFCs (chlorofluorocarbons) - residence time
100 years
dinitrogen oxide N₂O - activity that is increasing its concentration
car exhaust fumes
dinitrogen oxide N₂O - residence time
100 years
enhanced greenhouse effect
- increasing concentrations of greenhouse gases in atmosphere may be leading to an “enhanced” greenhouse effect
- may bring about an increase in temp on surface of planet, referred to as global warming
potential implications of global warming
climate change
rise in sea level
climate change
-more extreme weather conditions will develop eg. severe storms, drought in some areas, flooding
rise in sea level
- extra heat may lead to melting of polar ice caps
- add to climate change + causes rise in sea level
- greatest increase in volume of water in sea will be as direct result of extra heat
- will lead to water in oceans expanding, leading to flooding of low-lying areas of planet
benefits of enhanced greenhouse effect
-increase in rate of photosynthesis in plants
would come about due to increase in carbon dioxide levels in air
strategies for bringing reversal of increase in CO₂
- developing alternative energy sources other than fossil fuels
- growing many more trees worldwide
atmospheric pollution
air pollution
acid rain
air pollution
occurs when there is too much of a certain substance so that it may cause a significant hazard to present or future health or to the environment
acid rain
- rainwater naturally acidic due to presence of Carbonic acid (H₂CO₃) - from dissolved CO₂) pH 5.2
- acid rain is acidic rain caused by pollytion from SO₂ and NO₂
SO₂
- SO₂ present in air
- SO₂ reacts w/ oxygen in air to form sulfur trioxide SO₃
- sulfur trioxide then dissolves in rainwater to form sulfuric acid
NO₂
- oxides of nitrogen lead to acid rain
- prod by burning fossil fuels in power stations +high temps created by spark plugs in car engines. high temperature provides enough energy to cause nitrogen gas to combine w/ oxygen gas
- nitrogen monoxide combines w/ oxygen in air to form nitrogen dioxide
- nitrogen dioxide dissolves in water to form mixture of nitrous acid + nitric acid
harmful effects of acid rain
- damage to trees
- leaching of metal ions eg. aluminium, out of soil into lakes (can interfere with gill mechanism of fish, killing them)
- buildings + statues made of limestone eroded by acid rain
scrubbing systems
use of scrubbing systems in chimneys of power stations decreased incidence of acid rain caused by sulfur dioxide
calcium sulfite
SO₂ is made to combine w/ limestone to form calcium sulfite CaSO₃
limestone + sulfur dioxide –> cakcium sulfite + carbon dioxide
CaCO₃ + SO₂ –> CaSO₃ + CO₂
the ozone layer
- Trioxygen, O₃, a form of oxygen more commonly known as ozone.
- There is a layer of ozone surrounding Earth about 25 km above Earth’s surface
where the ozone layer is formed
- formed in stratosphere by reaction between an oxygen radical + an oxygen molecule
- oxygen radicals formed when ultraviolet light of particularly high energy breaks oxygen molecule into oxygen atoms
the ozone layer - oxygen radicals
- 2 oxygen radicals formed
- as soon as oxygen radicals formed, they react w/ the oxygen molecules in atmosphere to form ozone
- when ozone formed absorbs ultraviolet, photodissociation of ozone occurs. Ie. above reaction is reversed + ozone is decomposed
- some of oxygen radicals produced destroy ozone molecules by converting them to oxygen molecules
- oxygen molecules broken down by UV light to form oxygen radicals which lead to production of ozone
screening effect of ozone
reaction 2 responsible for the very important screening effect of ozone since it absorbs much of the harmful ultraviolet radiation
excessive exposure to UV light
causes skin cancer
ozone layer - oxygen radical - reaction 1
O* + O₂ –> O₃ (formation of ozone)
ozone layer - oxygen radical - reaction 2
O₃ –> O₂ + O*