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C8 (Homologous series (image, The alkanes, alkenes and cycloalkanes are…
C8
Homologous series
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The alkanes, alkenes and cycloalkanes are examples of homologous series. A homologous series is a group of chemicals which have similar chemical properties and can be represented by a general formula.
Hydrocarbons and homologous series A homologous series is a family of hydrocarbons with similar chemical properties who share the same general formula. We will look at three hydrocarbon series: alkanes, alkenes and the cycloalkanes. Hydrocarbons are compounds that contain only hydrogen and carbon.
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Cracking
Cracking is splitting up long saturated alkane molecules into smaller unsaturated alkene and alkane molecules which are more useful. Cracking is done by passing vaporized hydrocarbons over a powdered catalyst at about 400-700 degrees Celsius and 70 atm. Aluminium oxide is the catalyst used. The long chain molecules split apart or crack on the surface of the bits of catalyst.
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Fuels and pollutants
Human activities produce a number of gases that are released into the atmosphere. Most of these pollutant gases are produced by the burning of fuels. The burning of fuels releases a large amount of carbon dioxide into the atmosphere. This is thought to cause global warming. The incomplete combustion of fuels also releases small particles of solids, such as carbon, into the air. This makes buildings dirty and affects the lungs.
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Alkanes
The alkanes are a family of hydrocarbons that share the same general formula. This is: CnH2n+2 The general formula means that the number of hydrogen atoms in an alkane is double the number of carbon atoms, plus two. For example, methane is CH4 and ethane is C2H6. Alkane molecules can be represented by displayed formulae in which each atom is shown as its symbol (C or H) and the chemical bonds between them by a straight line.
Acid rain
Sulfur Dioxide causes acid rain. When fossil fuels are burned they release mostly CO2 which is a big cause of global warming. But they also release many other harmful gasses such as sulfur dioxide and various nitrogen oxides. The sulfur dioxide mixed with clouds and it forms dilute sulfuric acid. This then falls as acid rain. Acid rain turns rivers acidic killing fish.. The acid also kills trees and does damage to limestone structures. Finally it makes metal corrode faster.
The Earth's atmosphere
3 phases of the Earths atmosphere. Phase 1 -Volcanoes gave out steam and carbon dioxide. The water vapor eventually cooled down and formed the oceans. Phase 2 - A lot of the early carbon dioxide dissolved into the oceans. Nitrogen then was put into the atmosphere. Nitrogen isnt very reactive so the amount of nitrogen in the atmosphere will increase as ts not being broken down. Afterwards green plants started to take over the Earth. They photosynthesized using up lots of carbon dioxide and releasing oxygen. Phase 3 - The build up of oxygen in the atmosphere killed off early organisms that couldn't tolerate it. Evolution made use of the oxygen and not there is virtually no carbon dioxide left now.
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