Alkanes Flashcards
What are alkanes
Alkanes are a homologous series made up of saturated molecules which are joined by sigma bonds/single covalent bonds
are alkanes unreactive
yes
what is the general formula for alkanes
Cn H2n+2
what is a sigma bond
its a single covalent bond formed when two orbitals overlap end-to-end
what is a covalent bond
a shared pair of electrons
in an alkane how many sigma bonds does each carbon atom have?
4
each bond angle is
109.5 degrees (tetrahedral)
how is crude oil seperated into fractions
fractional distillation
why do the boiling points of alkanes increase?
London forces hold molecules together in solids and liquids but once broken the molecules move apart and the alkane becomes a gas. The greater the intermolecular forces the higher the boiling point.
If the chain length increases will the surface contact increase
Yes
Do you need more or less energy to overcome the greater london forces
more
Isomers of alkanes have the same molecular mass true or false
true
Do branched isomers have higher or lower boiling points than straight-chained isomers?
Lower
What are the factors that make alkanes unreactive?
-The C-C and C-H sigma bonds are strong
-The C-C bonds are non-polar
-The elecronegativity of carbon and hydrogen is so similar that it is considered non-polar
What do all alkanes react with?
A plentiful supply of oxygen to produce carbon dioxide and water
What is combustion?
It is a chemical reaction that involes burning the organic compounds
what do all combustion reactions give out?
heat
What are 3 reasons alkanes are used as fuels?
-They are readily available
-Easy to transport
-Burn in plentiful supply of oxygen without releasing toxic products
What is carbon monoxide?
A colourless odourless highly toxic gas
When does incomplete combustion occur?
When there is a limited supply of oxygen usually in a closed system.
What happens in the presence of sunlight (UV)
alkanes react with halogens
3 stages of the mechanism
initiation,propagation and termination
What happens in initiation?
the covalent bond in a halogen molecule is broken by homolytic fission. Each halogen atom takes one electorn from the pair forming two highly reactive molecules
What happens in propagation?
In the first step a halogen radical reacts with a C-H bond forming an alkyl radical and a molecule of hydrogen something
In the second step each alkyl radical reacts with another halogen molecule to form..
Then the new halogen radical reacts with another alkane and it goes on and on.
