Chapter 12-Alkanes Flashcards
What is the general formula for alkanes?
CₙH₂ₙ₊₂
Are alkanes saturated or unsaturated?
Saturated
What bond angles are around each carbon atom in alkanes and why?
- 109.5°
- 4 covalent bonds
What types of bonds to alkanes have?
Single C-C, C-H, Sigma (σ) bonds
What is a sigma bond?
An overlap of 2 orbitals with free rotation around it
As the chain length of an alkane increases what else changes and why?
Boiling point increases-more electrons so stronger london forces and more energy to overcome
As the branching increases of alkanes what else changes and why?
Boiling point decreases-molecules cant pack as closely together, fewer surface points of contact, weaker london forces, less energy to overcome
Why are alkanes unreactive?
Low polarity of C-H bonds and high C-C and C-H bond enthalpies
What reactions can halogens undergo?
- Combustion
- Can react with halogens
Why are alkanes good fuels?
Release lots of energy when burned
What is it called when alkanes burn with sufficient oxygen?
Complete combustion
What is the general symbol equation of complete combustion of alkanes?
CₙH₂ₙ₊₂ + (3n+1)/2 O₂ –>nCO₂ + (n+1)H₂
What is it called when alkanes burn with insufficient oxygen?
Incomplete combustion
What are the symbol equations for the 2 incomplete combustions of alkanes?
- CₙH₂ₙ₊₂ + (2n+1)/2 O₂ –>nCO + (n+1)H₂
- CₙH₂ₙ₊₂ + (n+1)/2 O₂ –>nC + (n+1)H₂
Why is CO toxic?
It bonds strongly and irreversible to haemoglobin in blood
What are the other harmful products of combustion (not CO)?
Nitrogen oxides (NOₓ) and sulfur dioxide (SO₂)
How are harmful products of combustion converted into less harmful products?
Using a catalytic converter
What do alkenes react with halogens to form?
Haloalkanes
What does the halogenation of alkanes requre?
UV light
What is the reaction mechanism of halogenation of alkanes?
Free radical substitution
What are the 3 steps of free radical substitution?
- Initiation
- Propagation
- Termination
What is the initiation step of free radical substitution involving chlorine and methane?
Cl₂ –(UV)–>2Cl.
What are the 2 propagation steps of free radical substitution involving chlorine and methane?
- CH₄ + Cl. –> .CH₃ + HCl
- .CH₃ + Cl₂ –> CH₃Cl
What are the 3 termination steps of free radical substitution involving chlorine and methane?
- Cl. + Cl. –> Cl₂
- .CH₃ + Cl. –> CH₃Cl
- .CH₃ + .CH₃ –> C₂H₆
What are the limitations of free radical substitution?
Mixture of products caused by:
* Substitution at a different part of the carbon chains
* Further substitution-multiple halogen atoms added
