Alkanes Flashcards
what is an alkane
a saturated hydrocarbon containing only C-H bonds
what is the general formula of an alkane
CnH2n + 2
are alkane bonds polar and why/why not
nonpolar as the carbon and hydrogens have similar electronegative
which intermolecular forces do they have and why
Van der Waals forces of attraction as the bonds are non polar
are alkanes soluble in water and why
insoluble in water because hydrogen bonds in water are stronger than alkanes van der waals forces of attraction
how reactive are alkanes
very unreactive
which reactions do alkanes undergo
combustion and reaction with halogens
what is crude oil, how is it formed and is it renawable
mixture of fractions with hydrocarbon of similar boiling points and properties
formed at high temperatures and pressures deep below the earths surface adn over millions of years and therefore is non-renewable
name the fraction from high to low boiling point
Gases
Petrol
Naptha
Kerosone
diesel
oil
fuel oil
bitumen
what is fractional distillation and how does it work
crude oil is heated and passed through a fractioning tower that has a heat gradient where it is cold at the top and hot at the bottom
vapours rise up the column and condense when the temperature is smaller than the boiling point
shortest chains condense at the top as they have the lowest boiling points
what is fracking and how is it done
natural gas that is held within rock is drilled into and HCL and methanol is added to break up the rock and collect the gas
what are the pros and cons of fracking
advantages:
- gas supply for many years
- reduces imported gas and electricity
disadvantages:
- chemical additives can pollute water
- can cause small earthquakes
why are alkanes cracked
turn long chain alkanes which are not economically valuable and turns them into shorter chain alkanes and alkenes
what are the conditions for thermal cracking
700-1200 K temperature
7000kPa pressure
what is the intermediate for the reaction
free radicals
what are the main products of thermal cracking
alkenes
what are the conditions for catalytic cracking
lower temp of 720K
lower pressure just above atmospheric
zeolite catalysts with honeycomb structure to give large SA
what are the main products of catalytic cracking
cycloalkanes, aromatic hydrocarbons and branches alkanes
write an equations for the combustion of propane
C3H8 + 5O2 —-> 3CO2 + 4H2O
what is a fuel
something which releases heat energy when combusted
what are the five main fuels compromising of alkanes
methane, butane, propane, petrol and paraffin
what is incomplete combustion and what products are formed in the case of alkanes
combustion in a limited supply of oxygen
it forms carbon monoxide and soot
which types of hydrocarbons are most likely to undergo incomplete combustion
longer chains
what is the environmental impact of carbon monoxide
toxic and poisonous
what is the environmental impact of nitrogen oxides
forms nitric acid which causes acid rain and smog
what is the environmental impact of sulphur impurities
form sulphuric acid and causes acid rain
what is the environmental impact of soot
asthma, cracking and global dimming
what is the environment impact of unburnt hydrocarbons
photochemical smog
what is the environmental impact of carbon dioxide
global warming
what is the environmental impact of water vapour
global warming
what are flue gases
gases given out by power stations
write two equations for two different ways of desulfurising flue gases
CaO + 2H2O + SO2 + 1/2O2 —-> CaSO4.2H2O
CaCO3 + SO2 + 1/2O2 —> CaSO4 + CO2
what are catalytic converters made up of
ceramic honeycomb coated with platinum, palladium and rhodium metals
what do catalytic converters catalyse
2CO + 2NO –> N2 + 2CO2
hydrocarbons + CO –> N2 + CO2 + H2O
what are greenhouse gases
gases which trap infrared radiation
what is the greenhouse effect
greenhouse gases trap infrared radiation in the atmosphere and the atmosphere heats up due to this
define carbon neutral activities
activities that produce no net carbon dioxide emissions
how are halogenoalkanes formed from alkanes
free radical substitution reaction
what are the three stages by free radical substitution
- initiation which is when the halogen bond breaks
- propagation which is when the chain part of the reaction where products are formed by free radicals remain
- termination where free radicals removed and stable products are formed
what are the conditions needed for the formation of a free radical chlorine atom
presence of UV light
write equations for the reaction of CH4 with Cl2
initiation: Cl2 —> 2CL.
propagation: Cl. + CH4 —> HCL + CH3.
CH3. + Cl2 —> CH3Cl + Cl.
termination:
.CH3 + Cl. –> CH3Cl
2Cl. –> Cl2
.CH3 + .CH3 –> CH3CH3
what is the ozone layers function
protects the earth from harmful exposure to too many UV rays
how do CFCs break the ozone layer down
free radical substitution
write an overall equation for the decomposition of ozone into oxygen
2O3 –> 3O2
write the free radical substitutions equations to show how Cl free radicals catalyse the break down of O3
Cl2 –> 2Cl.
Cl. + O3 —> ClO. + O2
ClO. + O3 –> 2O2 + Cl.
