Atmospheric Chemistry Flashcards
what is the atmosphere?
a layer of gases
atmospheric composition: nitrogen
78%
atmospheric composition: oxygen
21%
how does oxygen exist
as oxygen gas O2
and ozone O3
manufacture of oxygen 2
extracted from the atmosphere by;
- liquifying the air
- fractionally distilling the air
manufacture of oxygen
first step
air is filtered to remove dust particles
manufacture of oxygen
how is carbon dioxide removed?
air is passed through sodium hydroxide to remove CO2
manufacture of oxygen
how is water removed?
water vapour condenses out during compression and in drying towers using silica gel
manufacture of oxygen
what occurs during compression
the air heats up
manufacture of oxygen
how to cool air
the air is passed through a heat exchanger where it is cooled by cold nitrogen in a fractioning column
manufacture of oxygen
in fractioning tower
liquified air is distilled, oxygen collects at he bottom and nitrogen at the top
manufacture of oxygen
why is oxygen further purified
purified to remove inert gases such as neon and krypton
4 uses of oxygen
steelmaking
welding
medicine
recreational
steelmaking - use of oxygen
to remove carbon, silicon and phosphorous from cast iron as there oxides
welding - use of oxygen
when ethyne is burned in oxygen temperatures of about 3000ºC are reached
how is nitrogen found?
as N2
is nitrogen gas reactive or unreactive?
chemically unreactive due to the high bond energy of the triple bond between its atoms
why is nitrogen important
as it is a constituent of protein that is essential for muscle cells and blood cells
Natural Fixation of Nitrogen
any process that produces useful compounds from atmospheric nitrogen
3 natural fixation of nitrogen methods
lightning
bacteria
decomposition
how does lightning naturally fixate nitrogen?
at very high temperatures nitrogen and oxygen combine to form nitrogen monoxide, then combines with atmospheric oxygen to form nitrogen dioxide - dissolves in rain water to give nitrous and nitric acids, HNO2 and HNO3. fall on earth and deposited in soil, make plant protein
how does bacteria naturally fixate nitrogen?
certain species are capable of fixing atmospheric nitrogen into nitrates that plants can absorb to make plant proteins.
some are free in soil - Azotobacter, some in plants eg. clover and sweet pea - Rhizobium
how does decomposition naturally fixate nitrogen?
most of the nitrates in soil come from dead and decaying plants and animals
an example of an artificial fertiliser
ammonium nitrate
4 uses of nitrogen
freezing food
packaging of food
reduce the flammability of chemicals
manufacture of ammonia and nitric acid
how does nitrogen help with freezing food?
liquid nitrogen is used to fast freeze foods which is less damaging to food than normal freezing
how does nitrogen help with packaging food?
crisps are packed in nitrogen as it prevents oxidation of the oils
how does nitrogen reduce the flammability of chemicals?
nitrogen is used to reduce the oxygen content in storage tanks, thus reducing the flammability of certain chemicals
it is also used to flush out dangerous vapours in tanks
manufacture of ammonia
nitrogen is used as feedstock in the manufacture of ammonia
equation for how lightning naturally fixates nitrogen
N2 + O2 -> 2NO
heat change of how lightning naturally fixates nitrogen
endothermic
shape of CO2
linear
Combustion of carbon dioxide eqn.
C + O2 -> CO2
carbon dioxide as an acid in water
CO2 + H2O -> H2CO3
H2CO3
carbonic acid (weak)
what does aqueous carbon dioxide form?
an equilibrium mixture containing hydrogen ions, carbonate ions and hydrogen carbonate ions
2 equations for equilibrium mixture containing hydrogen ions, carbonate ions and hydrogen carbonate ions
H2CO3 ⇌ H+ + HCO3-
H2CO3 ⇌ 2H+ + CO3 2-
can carbonic acid be isolated as a single substance ?
no
4 uses of carbon dioxide
carbonated drinks
fire extinguishers
cooling agent (dry ice)
in the manufacture of urea
what type of fire would you put out with carbon dioxide?
electrical
when is carbon monoxide formed?
if carbon is burned in a limited supply of oxygen
formation of carbon monoxide eqn.
C + 1/2 O2 -> CO
what type of oxide is carbon monoxide
neutral oxide - does not react with water
why is CO poisonous
it deprives the body of oxygen
where is CO present?
in cigarette smoke and car exhaust fumes
fermentation of glucose equation
C6H12O6 -> 2C2H5OH + 2CO2
enzyme for fermentation of glucose
zymase
greenhouse gasses
gases in the atmosphere that absorb infra-red radiation from the sun
examples of greenhouse gases
carbon dioxide methane water vapour nitrous oxide ozone CFCs
how much of the atmosphere is CO2
0.035%
most abundant greenhouse gas
CO2
what accounts for the increase in CO2
burning of fossil fuels and deforestation
what reduces CO2
absorbed by oceans
what accounts for more water vapour
global warming
what can help to block sun rays
in increase of water in clouds
concentration of methane in atmosphere
1.7 ppm
why is there an increase in methane
waste from homes cattle populations swamps, bogs and paddy fields aerobic fermentation trapped in ice - melting
how effective is methane
20 times more effective than CO2
how effective are CFCs
40 times more effective than CO2
problem with CFCs
the breakdown of CFCs in the atmosphere release chlorine radicals that break up the ozone layer
what is the ozone layer responsible for?
for protecting the earth from uv radiation
residence time of CO2
50 to 200 years
residence time of methane
10 years
residence time of CFCs
50 to 100 years
4 possible implications of the increased greenhouse effect
rise in sea levels
extinction of some plants
increase in levels of CO2 and methane
disruption to agriculture
3 sources of air pollution
domestic
industrial
vehicles
describe domestic pollution
fuels contain sulfur and carbon and when burned from sulfur dioxide and carbon dioxide. SO2 dissolves in water to produce acid rain, which kills vegetation and damages buildings, increased CO3 cause an increase in global temperature. smoke and dust particles are produced which cause smog which blackens buildings and can cause respiratory problems
describe industrial pollution
the fuels used in industry e.g. oil and natural gase, release sulfur dioxide and carbon dioxide
describe vehicle pollution
exhaust fumes produce unburned hydrocarbons, carbon monoxide and the oxides of nitrogen and lead
nitrogen monoxide and nitrogen dioxide cause acid rain and respiratory problems. Leas and its compounds are toxic and affect the brain. (catalytic converters)
when is acid rain caused
when gases such as carbon dioxide, nitrogen dioxide and sulfur dioxide dissolve in water to form carbonic acid (H2CO3), nitrous acid (HNO2) and sulfurous acid (H2SO3)
effects of acid rain on the environment
corrosion of buildings reduction of crop yield extinction of some plants leaching of heavy metals from soil reduction of fish numbers when snow melts into water
3 preventative measures against acid rain
reduction in use of fossil fuels
use of catalytic converters
scrubbing of waste gases using limestone to remove pollutants from waste gases
ozone
triatomic form of oxygen, O3
describe ozone
a pale blue gas that is pleasant at low concentrations but is toxic at high concentrations and damages plant life
significance of ozone layer
ozone protects life on earth from ultra-violet radiation
formation of ozone
ultra-violet radiation breaks up oxygen molecules into oxygen free radicals, they then combine with molecules of oxygen to form ozone
formation of ozone eqn.
O2 -> 2O•
O• + O2 -> O3
photodissociation of ozone
destroyed by uv light
constantly being formed and broken up, usually at a steady rate
photodissociation of ozone eqn.
O3 -> O2 + O•
uses of CFCs
solvents in dry-cleaning
refrigerators and air conditioning - coolants
aerosols
stratosphere
upper atmsophere
eqn. for breakdown of CFCs in the stratosphere
n
removal of ozone
reactive chlorine atoms break up ozone to form oxygen and chlorine monoxide, that reacts when oxygen to form chlorine
equation for removal of ozone
Cl• + O3 -> ClO + O2
ClO + O• -> Cl• + O2
i single chlorine atom
can destroy 1 million ozone molecules
oxygen atoms destroying ozone eqn.
O• + O3 -> 2O2
nitrogen monoxide destroying ozone
NO + O3 -> NO2 + O2
eqn. for methane absorbing chlorine
CH4 + 2Cl -> CH3Cl + HCl
