Chemical Properties of Carbon Compounds

Summary

 Carbon compounds undergo different types of chemical reactions.

Combustion:
All carbon compounds react with oxygen to produce heat and light along with carbon dioxide and water. This reaction of carbon with oxygen is called combustion.

Carbon Compound + Oxygen → Carbon dioxide + water + heat and light
CH4 + 2O2 → CO2 + 2H2O + Heat and light. 

  • Aliphatic compounds on combustion produce a non-sooty flame.
  • Aromatic compounds on combustion produce sooty flame.


Oxidation:
Alcohols undergo oxidation in presence of oxidising agents like alkaline potassium permanganate 
or acidified potassium dichromate to form carboxylic acids. 
Example:
Ethyl alcohol on oxidation with alkaline potassium permanganate or acidified potassium dichromate gives acetic acid.

CH3-CH2-OH      Alkaline KMnO4 or Aicidified K2Cr2O7     CH3-COOH


Addition reaction:
A chemical reaction is said to be an  addition reaction if two substances combine and form a third substance.
Unsaturated hydrocarbons undergo addition reactions. In addition reactions molecules add across double bond or triple bond.  
Example: 
Hydrogenation reaction involves the addition of hydrogen to unsaturated hydrocarbons in presence of catalyst like nickel or platinum to form saturated hydrocarbons.

 CH2 = CH2 + H2        Ni or Pt         CH3-CH3

 CH ≡ CH + 2H2         Ni or Pt          CH3-CH3

Addition of halogens to alkenes.

CH= CH2 + X2 → CH2X - CH2


Substitution reaction:
A reaction in which an atom or group of atoms replaces another atom or group of atoms is called substitution reaction. Alkanes undergo substitution reactions. 
Example: 
Chlorination of methane in presence of sunlight gives a mixture of products like methyl chloride, 
methylene chloride, chloroform and carbon tetrachloride.
 
CH4 + Cl2      Sunlight       CH3Cl + HCl
CH3Cl+Cl2         Sunlight        CH2Cl2 + HCl
CH2Cl2+Cl2       Sunlight        CHCl3+HCl
CHCl3+Cl2       Sunlight         CCl4+HCl


Polymerization reaction:
Alkenes and alkynes at higher temperatures under polymerization to form bigger molecules called as polymers.
Example:
Ethene at 400 °C undergoes polymerization to form polyehene.

nCH= CH2 → [-CH-CH- CH- CH2-]n

Cracking:
At higher temperatures in absence of air higher hydrocarbons breaking into smaller hydrocarbons. This process is called cracking.
Example:
 
              C10H22           Cracking at 600 - 700          C6H14  +  C4H8

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