alkanes Flashcards
(19 cards)
what is a sigma bond
a type of
covalent bond where the
electrons are shared on a
line directly between the
two bonded atoms.
what is the trend in boiling points of alkanes
As the chain length increases, the molecules have a larger surface area, so more surface contact is possible between molecules.
Therefore, the London forces between the molecules will be
greater and so more energy is required to overcome the forces.
what is crude oil
a mixture containing mostly straight and branched chain alkanes
name the products and their uses of fractional distillation of crude oil from highest melting point to lowest melting point
-Bitumen (roads and roofs)
-fuel oil (ships, power stations)
-diesel oil (fuels for cars, lorry’s buses)
-kerosene (aircraft fuels)
-naphtha (making chemicals)
-gasoline (fuel for cars)
-refinary gases (bottled gas)
what is the trend in characteristics of the products of crude oil fractional distillation as the melting point decreases
-lower number of carbons
-lower BP
-very volatile
-less viscous
-ignites easily
what is the effect of branching on boiling point
Less contact between branched molecules
🡪 WEAKER London forces
🡪 LOWER boiling point
why is combustion an important reaction
- they are an effective energy source for use as fuels.
-because they have a high energy content and combustion is an exothermic
reaction which releases heat energy.
what is incomplete combustion
Incomplete combustion occurs when there is not enough oxygen present to
allow complete combustion.
what are the products of incomplete combustion
- carbon monoxide and water.
- carbon and water
what is the dangers of incomplete combustion
Carbon monoxide is TOXIC →restricts the effectiveness of the blood to transport oxygen in the body.
* because carbon monoxide binds irreversibly to haemoglobin preventing oxygen from binding and being transported
* Tissues can become starved of oxygen causing death
what must cars be to ensure
that the volume of carbon monoxide in the exhaust is within prescribed limits
Car engines must be well ventilated and effectively tuned
what is the test for distinguishing between an alkene and alkane
-Bromine water (an orange solution of bromine)
-It becomes colourless when it is shaken with an alkene.
-Alkenes decolourise bromine water, but alkanes cannot.
describe and explain the reactivity of alkanes
low reactivity due to the low polarity of the C-H/C-C bond (non-polar molecules) and the fact that C-H/C-C are relativity strong requiring a lot of energy to break.
how does alkanes react with halogens
-radical substitution
-react very slowly
-only in the presence of UV light
what is homolytic fission
A Covalent bond breaks and one electron goes
to each of the bonding atoms.
what is a radical
An atom or group of atoms with an unpaired electron
what is halogenisation
-substitution of a hydrogen
atom in the alkane with a halogen
what are the stages of radical substitution in order
- initiation–> radical formed
- propagation–> maintains the reaction by forming one of the products and a new radical
-termination–> Ends the reaction by removing the radicals and forming molecules
