C12 - Alkanes Flashcards
What is the general formula pf alkanes?
CnH2n+2
What are alkanes mainly used for?
Fuels
What type of covalent bond is present in alkanes?
Sigma bond
What is a sigma bond?
Head on overlap of two orbitals, one from each bonding atom
Two electrons shared
What is a covalent bond
Strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms
Where is the bond positioned in a sigma bond?
Line directly between the two bonded carbon atoms
How many sigma bonds does a carbon atom have?
4
either C-C/C-H
What is the shape and bond angle of alkanes?
Tetrahedral
109.5
How is crude oil seperated?
Fractional distillation
What is fractional distillation?
Separation of components in a liquid mixture by their different boiling points into fractions with different compositions
Effect of chain length on boiling point
-Inc chain length
-Greater surface area of contact
-Stronger London forces
-Req more energy to overcome
Effect of branching on boiling point
-More branching
-Less surface area of contact
-Weaker London forces
-Req less energy to overcome
Are alkanes reactive?
Not really
Why aren’t alkanes reactive?
-Sigma bonds in C-C and C-H are strong
- C-C bonds are non-polar
- C-H bonds considered non-polar due to similar electronegativity value
Equation for complete combustion of alkanes?
CnH2n+2 + O2 –> CO2 + H2O
Equation for incomplete combustion of alkanes?
CnH2n+2 + O2 –> CO + H2O
What is the molar gas volume formula?
volume = molar gas volume (24dm^3) x amount
V = Vm x n
What are the conditions and products of the reaction of alkanes with halogens
alkane + halogen –> haloalkane + hydrogen halide
UV radiation
What is the mechanism for the halogenation of alkanes?
Free radical substitution
What are the three stages of radical substitution?
Initiation
Propagation
Termination
What happens during initiation?
Covalent bond broken by homolytic fission
Under UV radiation
Forms to halide radicals
What happens during propogation?
Chain reaction involving two steps
1) Halide radical reacts with C-H bond, forming a new radical and a hydrogen halide
2) New radical reacts with halogen molecule to form the new organic product and a halide radical
(can continue until all the reactants are used up)
What is a chain reaction?
Reaction in which the propagation step releases new radicals that continue the reaction
What happens during termination?
All radicals combine in pairs forming 3 compounds
What are limitations of radical substitution?
-Further substitution
-Substitution at different points on the carbon chain
