The reaction of alkanes - ppt slide presentation

 

Organic Chemistry
Part 3 – Chemical Reaction of The Alkanes

Substitution Reaction

• A substitution reaction is a reaction in which an atom or a group of atoms is replaced by another atom or group of atoms.

• Alkanes react with chlorine in sunlight as their hydrogen atoms are substituted by chlorine atoms.

• Methane + chlorine 🡪 chloromethane+                   hydrogen chloride

CH4(g) + Cl2(g) 🡪 CH3Cl(g) + HCl(g)

the reaction with the help of sunlight

• Chlorofluorocarbons (CFCs) are group of chemically unreactive compounds that have been widely used as solvent that vaporise easily.

• The uses of CFCs : Propelant in aerosol cans, cleaning solvent, refrigerant & ac, blowing agent.

• The most used CFCs was CFC-12 (dichlorodifluoromethane CF2Cl2)

Another free radical

• Ultraviolet light splits chlorine molecules into separate energised atoms (free radical). These free radicals then react with ozone to form oxygen, these reduce amount of ozone layer over various region of the earth, allows a greater amount of harmful ultraviolet radiation.

•  O3(g) + Cl(g) 🡪 OCl(g) + O2(g)

Another free radical

Combustion of alkanes

• Alkanes burn completely in oxygen to form carbon dioxide and water.

CH4(g) + 2O2(g) 🡪 CO2(g) + 2H2O(l)

• Incomplete combustion produces carbon monoxide and also soot (unburt carbon)

2CH4(g) + 3O2(g) 🡪 2CO(g) + 4H2O(l)

CH4(g) + O2(g) 🡪 C(s) + 2H2O(l)