Chapter 12: Hydrocarbons

  • Explain why the systematic method of naming chemical compounds is necessary.
  • Characterize a hydrocarbon. Draw electron cross and dot structures of simple alkanes.
  • Write a chemical equation to show the preparation of alkanes from the hydrogenation of alkenes and alkynes and the reduction of alkyl halides.
  • Draw structural formulas of alkanes, alkenes, and alkynes up to 5 carbon atoms.
  • Write a chemical equation to show the preparation of alkenes from dehydration of alcohols and dehydrohalogenation of alkyl halides.
  • Write a chemical equation to show the preparation of alkynes from dehydrohalogenation of 1, 2- dihalides, and dehalogenation of tetrahalides.
  • Write chemical equations showing halogenation of alkanes, alkenes, and alkynes.
  • Write chemical equations showing the reaction of KMnO4 with, alkenes and alkynes.

The simplest organic compounds are hydrocarbons. The organic compounds which contain only two elements, carbon and hydrogen are called hydrocarbons. There are several kinds of hydrocarbons. They are classified according to the type of bonding between the carbon atoms. You have learnt differences between alkanes, alkenes and alkynes in the previous chapter.

  Do you know?   Caron dioxide and other gases in the air let the sun rays in, to warm the surface of earth. When the earth tries to radiate this heat back into the space, molecules of these gases trap this energy.

            About 90% of the energy used to sustain our way of life comes from fossil fuels. Coal, natural gas and petroleum are called fossil fuels. Why are these fuels called as fossil fuels? Natural gas is a mixture of low molecular weight hydrocarbons. Mainly it contains methane. Petroleum is a liquid mixture of mainly hydrocarbons. When these fuels are burnt, they produce carbon dioxide, water and heat. It has been estimated that the concentration of carbon dioxide in the atmosphere has increased up to 20% by the end of twentieth century.

Carbon dioxide and other gases produce a greenhouse effect). About 25 billion tons of carbon dioxide is released into the atmosphere each year, 22 billion tons of it comes from the burning of fossil fuels. About 15 billion tons per year are removed by the plants. Thus 10 billion tons of carbon dioxide remains in the air. This is causing global warming. (For detail see section 14.3.1)

Although hydrocarbons burn, many of them are not generally used as fuel. They are also used as feedstock in industry. These hydrocarbons are starting raw materials for the synthesis of a large number of organic compounds. These compounds have commercial importance.

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