12. Alkanes Flashcards
Whats the general formula for alkanes?
CnH2n+2
What are the simplest form of hydrocarbons?
Alkanes (methane)
How is a sigma bond formed?
The direct overlap of two orbitals, one from each bonding atom
Why are alkanes not rigid?
They have free rotation around sigma bonds
How are alkanes seperated and what property allows this method of seperation?
Fractional distillation, can be used as alkanes have differing boiling points
How does chain length affect an Alkanes boiling point?
Longer chain, greater surface area of contact, stronger london forces, more energy required to overcome forces, increased boiling point
How does branching affect Alkane boiling point?
Branched chains have less surface area pf contacts, weaker London forces, less energy needed to over come forces, lower boiling point than there straight chained isomers
Why are Alkanes unreactive?
- Strong sigma bonds
- C-C bonds are non polar
- C-H bonds are non polar as have similar electro negativities
Why are Alkanes used as fuels?
Easy to transport
Readily available
Burn in a plentiful supply of oxygen without forming toxic products
Describe complete combustion of Alkanes
In a plentiful supply of Oxygen alkanes burn completely to form carbon dioxide and water
Describe incomplete combustion of Alkanes
When oxygen supply is limited Alkanes oxidise to water but form toxic carbon monoxide (CO) or soot (C)
Why is Carbon Monoxide dangerous?
Highly toxic
Odourless and colourless so hard to recognise
What reagents are required for Alkanes to form Haloalkanes?
UV light and halogen
What mechanism is used when Alkanes form Haloalkanes?
Free radical substitution
What are the three steps in radical substitution
Initiation
Propogation
Termination
