alkanes Flashcards
mps on mp/bp is alkanes
simple molecular compounds
IMF breaks-> London forces only
Weak = low boiling point
describe why mp/bp increases with length of chain of straight chain alkanes
the longer the carbon chain
the more electrons
higher london forces
melting point increases
how do straight chain alkanes interact
they stack- lots of contact between chains
give the equation for complete combustion of an alkane
alkane + oxygen -> CO2 + H2O
describe why branched alkanes have lower melting points
cannot stack as well
fewer points of contact between molecules
less energy required to break London forces
what type of bonds are alkanes heavy in
sigma bonds
give the equation for incomplete combustion of alkanes
alkane + less O2 -> CO + H2O
advantages of complete combustion of alkanes 3
most efficient
most exothermic
doesn’t release dangerous products
give the equation for really incomplete combustion of alkanes
Alkane + even less O2 -> C(s) + H2O
what are the 2 main alkane reactions
combustion
free radical substitution
define a free radical
a species with an unpaired electron
define substitution
one atom within a compound leaves, and something new takes its place
how to represent an unpaired electron on an element
a dot
how are free radicals formed
bond between diatomic element is broken, leaving 2 free radicals
what is the name of the bond breaking to form a free radical
homolytic fission
what 2 things do you need to know for free radical substitution
the reaction
mechanism (short intermediate steps)
name the 3 mechanism stages in free radical substitutions
1 initiation
2 propagation
3 termination
describe what happens in the propagation stage of free radical substitution
main reaction
uses both reactants and generates both products
describe what happens in the initiation stage in free radical substitution
reaction starts by needing UV light
breaks the larger/weakest bond
breaking halogen
describe the termination stage of free radical substitution
takes free radicals and gets rid of them
why are free radicals bad 3
- multiple substitution reactions
- don’t know where which carbon the substitution will take place on
- you make unwanted side products - products in the termination step
why is free radicals producing multiple substitution reactions bad and how to stop it
it’s difficult to control
put it in the dark (taking energy away)
why is making unwanted side products a bad thing
they are unwanted and therefore a waste of matter
why is only a small amount of the halogen used in radical substitution reactions
it keeps regenerating in reactions
