3.3.2.4 Chlorination of alkanes

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Ebi

Cards (21)

  • What process is bond breaking
    Endothermic
  • Name the 2 types of bond breaking
    Heterolytic and homolytic fission
  • What does homolytic fission produce
    Free radicals
  • What does heterolytic fission produce?
    Ions
  • What happens in homolytic fission?
    One pair of the shared electrons goes to each atom, both atoms have one unpaired electron
  • What happens in heterolytic fission?
    Both of the electrons of the shared pair goes to just one of the atoms forming +ve and -ve ions
  • Note to remember in homolytic fission?
    Occurs in gas phase or non-polar solvents, free radicals are highly reactive
  • Note to remember in heterolytic fission?
    Occurs in polar solvents, bond that break is often polar, e.g Cl-Cl or C-Br
  • Conditions for alkanes to react with chlorine and bromine?
    Heating or exposure to ultraviolet light
  • What is free radical substitution?
    Replacement of hydrogen atoms in a molecule by halogen atoms in a reaction involving free radicals
  • Name the 3 phases in free radical substitution?
    Initiation, propagation, termination
  • What occurs in initiation?
    Homolytic fission of bonds to form free radicals, only occurs in ultra-violet light
  • Conditions for inititation?
    Ultra-violet light
  • What occurs during propagation?
    Free radical reacts, but produces another free radical like a chain reaction
  • What occurs during termination?
    2 free radicals combine, to form a stable molecule, 2 unpaired electrons form a covalent bond
  • What is unique about the propagation phase?
    Releases heat, chain reaction, exothermic reaction
  • Role of ultra-violet light play in free radical mechanism
    Provides energy needed to overcome to activation energy needed to break the bonds homolytically.
  • Propagation formation of CH3. and reformation of Br.
    CH4 + Br. = CH3. + HBr
    CH3. + Br2 = CH3Br + Br.
  • Formation of methane in the termination phase
    CH3. + H. = CH4
  • Methane to triiodomethane
    CH4 + I2 = CHI3 + HI
  • Explain the chlorine molecule is not polar
    Has no lone pairs, similar electronegativity, cancel each other out, equally shared