A fuel is a substance that reacts with oxygen to release useful energy.
The complete combustion of any hydrocarbon in oxygen will only produce carbon dioxide and water as waste products which are both clean and non-poisonous.
HYDROCARBON + OXYGEN ----> CARBON DIOXIDE + WATER (+ energy)
CH4 + 2O2 ----> 2H2O +CO2
When combustion is complete gas burns with a clean blue flame.
If there isn't enough oxygen combustion will be incomplete. This gives carbon monoxide and carbon as waste products, and produces a smoky yellow flame.
Phase 1 - Volcanoes gave out steam and carbon dioxide.
The Earths surface started off molten so any atmosphere was boiled away.
Then it cooled and a thin crust formed, but volcanoes kept erupting releasing gases. This degasing produced ammonia and steam but mostly carbon dioxide.
When things settled down the early atmosphere was mostly carbon dioxide and water vapour (later condensed to form ocean).
Phase 2 - Green plants evolved and produced oxygen
A lot of early carbon dioxide dissolved into the oceans.
Green plants evolved and photosynthesised which removed carbon dioxide and replaced it with oxygen. Thanks to this the air became mainly oxygen
Lots of carbon dioxide was locked in fossil fuels and sedimentary rocks.
Nitrogen was put into the atmosphere as a result of oxygen reacting with ammonia and released by denitrifying bacteria.
Phase 3 - Ozone layer allows evolution of complex animals.
The build up of oxygen killed off many early organisms but allowed the evolution of more complaex ones.
The oxygen also created the o-zone layer which blocked harful rays.
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The carbon cycle
The carbon on Earth moves in a big cycle.
Resperation, combustion and decay of plants and animals add carbon dioxide to the air and remove oxygen.
Photosythesis removes carbon dioxide and oxygen
This should balance out but human activity has unbalnced the cycle.
Increased population means increased levels of carbon dioxide beacuse:
More energy/ fuel is need
More countries are becoming industrial
More people have cars.
MOre land is needed which means more trees are cut down.
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Air polution and acid rain.
Acid rain is caused by sulfur dioxide and oxides of nitrogen.
Sulfur dioxide comes from impurities in rocks released during the burning of fossil fuels.Nitrogen oxides are created from a reaction between nitrogen and oxygen in the air caused by heat of the burning.
When these gases mix with clouds they form dilute sulfuric and nitric acid.
Power stations and internal combustion are the main causes of acid rain.
Acid rain kills fish by getting into lakes, trees, damages limestone buildings and corrodes metal.
Oxides of nitrogen cause a photochemical smog its air polution caused by sunlight. These oxides combine with oxygen to create ground ozone which causes breathing difficulties, headaches and tiredness
Carbon monoxide is a poisonous gas that combines with haemoglobin in the blood and stops it carrying oxygen. Carbon monoxide is caused by incomplete combustion
Catalytic converters use a catalyst platinum and rhodium to reduce harmful gases from internal combustion being released.
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