Alkanes Flashcards
Generic formula for alkanes
C(n)H(2n+2)
Describe the bonding of alkanes
Single covalent sigma bond
Fully saturated
Can rotate
What is a sigma bond
End to end overlap of orbitals
Single covalent bond
Describe the shape of alkanes
Tetrahedral (4 bonds per carbon atom)
Bond angle in alkanes
109.5
What effect does increasing the length of the carbon chain have on boiling point? Why?
BP increases
More surface contact points so stronger London forces
What affect does increasing branching have on boiling point? Why?
Decrease BP
Less compact, weaker and fewer London forces
Less surface contact points, weaker London forces
Describe the reactivity of alkanes and state why
Lack of reactivity
Due to strong sigma bonds and lack of polar bonds
Why are alkanes used as fuels?
Readily available
No toxic byproduct when combusted
Easy to transport
What may form in incomplete combustion?
CO or C
(not both)
+H2O
Give an example of a substitution reaction with alkanes
+ Halogen
Halogen substitutes H
State steps in radical substitution
Initiation
Propagation
Termination
Explain radical substitution
A Halogen radical substitutes a H in a hydrocarbon
Describe initiation
Covalent bond in Halogen is broken by homolytic fission is presence of UV radiation
What occurs during initiation?
Photodissociation
What does hv mean?
Light
Describe Propagation
A stable and radical react to form a different stable and radical
Atom from stable goes to radical
Describe Termination
Two radicals react to form a stable
Two unpaired electrons form a pair
What are the limitations of radical substitution?
Further substitution of H with Halogen leads to undesired haloalkanes (multiple Halogen groups)
Substitution of Halogen at different points gives rise to structural isomers
Gives two names of Hcl and the conditions
Aqueous = hydrochloric acid
Solid/ gas = hydrogen chloride
Define chain reaction
When a species is used up in one reaction and then produced in a second one leading to a cycle of the two reactions
Why is further substitution not desired?
Produces a mixture of structural isomers which are costly and time consuming to seperate