- 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.
- HYDROCARBON + OXYGEN ----> CARBON DIOXIDE + WATER + CARBON MONOXIDE + CARBON
- Carbon monoxide is a colourless, poisonous gas
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The evolution of the atmosphere
- 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.
- CARBON MONOXIDE + NITROGEN OXIDE---->NITROGEN + CARBON DIOXIDE. 2CO + 2NO ----> N2 + 2CO2
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