alkanes: content

Question 1

general formula for alkanes

Answer 1

CₙH₂ₙ₊₂

Question 2

general formula for cycloalkanes

Answer 2

CₙH₂ₙ (same as alkenes)

Question 3

how are alkanes bonded

Answer 3

sigma (σ) bonds (strongest type of covalent bond)

Question 4

complete combustion equation

Answer 4

alkane + oxygen → carbon dioxide + water

Question 5

equations for incomplete combustion

Answer 5

alkane + oxygen → carbon monoxide + water
alkane + oxygen → carbon + water

Question 6

issues with incomplete combustion

Answer 6

• less exothermic than complete combustion
  
  • less cost-effective
• carbon monoxide forms dative covalent bonds to haemoglobin
  
  • irreversible and strong
  • reduces blood oxygen concentration and blocks cell respiration

Question 7

free radical substitution: overall equation

Answer 7

halogen + alkane →UV light→ haloalkane + hydrogen halide
(substitution reaction)

Question 8

free radical substitution mechanism

Answer 8

initiation (creating free radicals)
X₂ →UV light→ 2X⋅

propagation (molecule + radical → molecule + radical)
1ˢᵗ: CₙH₂ₙ₊₂ + X⋅ → ⋅CₙH₂ₙ₊₁ +HX
2ⁿᵈ: ⋅CₙH₂ₙ₊₁ + X₂ → CₙH₂ₙ₊₁ +X⋅
this step is self-propagating and will continue until you run out of reactants

termination (two radicals combine to form a molecule)
two halogen radicals combine
a halogen radical combines with an alkyl radical
two alkyl radicals combine

Question 9

issues with free radical substitution

Answer 9

yields tend to be low
- further substitution can occur, forming a mixture of difficult-to-isolate products
- substitution can occur in different positions, creating position isomers