Document page
chemistry igcse acapprinted 107 · PDF 107
145 pagesrevision 46934
printed 107 · PDF 107
Page image rendered from the stored file at 110 dpi; it sharpens as you zoom. Outlines are placed from each region’s stored position on the page (612 × 792 pt).
readable
Source of this text: embedded text layer. The better of the embedded text and OCR is kept.
107
Examples :
Substitution Reactions with Halogens
Alkanes react with halogens in the presence of ultraviolet light.
The Halogen atom replaces a hydrogen atom bonded with a carbon in the chain
Given that the halogen is in excess , one by one , all the hydrogens can be replaced
So Methane would , after 4 reactions , form Carbon Tetrachloride
Example: CH₄ + Cl₂ → CH₃Cl + HCl (Methane reacts with chlorine to form chloromethane and
hydrogen chloride)
Cracking of Alkanes
Cracking is the process of breaking down long-chain alkanes into shorter alkanes and alkenes. This
is done to increase the supply of shorter, more useful hydrocarbons and produce alkenes, which are
valuable for making plastics.
Types of Cracking:
Catalytic Cracking: Lower temperatures (450°C) and slight pressure with a catalyst (zeolite).
Produces mainly branched alkanes and aromatic hydrocarbons.
Example Reaction:
Hexane (C₆H₁₄) → Butane (C₄H₁₀) + Ethene (C₂H₄)
C₆H₁₄ → C₄H₁₀ + C₂H₄
Purpose: Cracking produces alkenes for polymers and provides fuels for gasoline, which burns
more efficiently in car engines.