CHE4: ISOMERISM

This unit describes the formation of isotherms in chemical elements

Existence of two or more compounds with different structural formula but same molecular formula

The different compounds are called isomers.

Alkenes

Physical properties of Alkenes

– The first five members are gases the next 12 members are liquid and the rest are solid.

– They are immiscible with water (when mixed they form 2 separate buyers)

– They are less dense than water.

 Boiling points

They increase with increase in molecular size (increase in molecular weight).

Chemical properties

Methane burns in limited air to give carbon monoxide gas and water vapour or carbon (pluck particles) and water vapour.

2(CH4 (g) + 02(g)                                                         C0g + 2H20(g)

2CH4 (g) + 302(g)                                                       2C0 (g) + 4H20(g) then (1)……………….. (1)

CH4g + 02g                                                           C(S) + 2H20(g) then    (i)……………………. (ii)

 

Combustion of Methane and other hydrocarbons in limited air is a source of pollution.

The pollutants introduced in the air are:

  • Carbon monoxide (poisonous gases)
  • Carbon particles
  • Unburnt hydrocarbons

Combustion of Methane in excess air. The products are: carbon dioxide and water vapour.

CH4 (g) + 202(g  )                                                                                  C02(g) + 2H20 (g then L)

Alkenes are saturated hydrocarbons.

 Saturated hydrocarbon

This is one in which all carbon –carbon bonds are single:

PETROLEUM

The name petroleum means rock oil. It comes out of the grounds as a thick green or dark brown liquid .Oil deposits are usually found with sand, salt and brine, sulphur .Oil was formed from the remains of microscopic plants and animals which lived in warm inland seas million of years ago. The chemical effects of pressure, heat and bacteria converted the remains into oil just as they converted forests into coal

Oil is usually found in the porous rock layer e.g. sandstone, between 2 layers of non-porous rock. Natural gas is above the oil .This is a mixture of many gases but contains between 80 and 99 percent of methane.

Fractionation of Crude oil (Petroleum)

Petroleum is a mixture of alkenes; it is separated by fractional distillation. Each fraction is a mixture of various alkenes.

distilling

First fractions are light coloured, volatile, highly flammable, not viscous (flow easily like water). Higher fractions are ark coloured, hot flammable, have high viscosity not volatile.

petroleum

Cracking of Oils

Reaction which involves converse of long hydrocarbons into smaller hydrocarbons (smaller molecules) of petrol and gases. (Mainly alkenes and hydrogen)

C10 H22 (oil)                                             C7H16 (petrol) + C3H6 (g)                  


Homologous Series

  • A group of compounds with similar structure and similar properties.
  • They confirm the same general formulae e.g.

Cn H2n for alkenes

Cn H2n for alkenes

Cn H2n for alkynes

  • They can be prepared by similar methods
  • They show a gradual change of physical properties.

THIS VIDEO EXPLAINS MORE ABOUT ISOMERISM

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ASSIGNMENT : ISOMERISM MARKS : 10  DURATION : 1 week, 3 days

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