alkanes Flashcards
unburnt hydrocarbons
are toxic and can cause cancer if breathed in
thermal cracking
high temp - 700-1200K
high pressure - 7000KPa
always produce one alkane and all other molecules being alkenes
sulphur dioxide - SO2
when sulphur burns sulphur dioxide is produced
S(s) O2(g) —-> SO2(g)
sulphur dioxide dissolves in rainwater to form acid rain
SO2(g) + 0.5O2(g) + H2O(l) —-> H2SO4(l)
this can erode buildings and statues, killing plants and trees and killing fish through contamination of lakes
process of fractional distillation
-crude oil is heated to vapourise and enters the column
-hydrocarbons have different boiling points
-boiling points differ on size/mr/chain length
-the column is cooler at top+ hotter at the bottom
-larger molecules with higher boiling points condense at the bottom
pollution - chemical produced and polluting effect
CO2 - greenhouse gas
H2O - greenhouse gas
CO - poisonous
Solid C - damages the lungs
physical properties of alkanes
chain length
-alkanes have IDD between molecules
-strength of attraction increases with increasing size of molecules + number of electrons
-longer the c chain the bigger the molecule and more electrons
branching
-less branching = more surface contact area between molecules so IDD attractions between molecules
Nitrogenous oxides
high temps in cars can cause nitrous oxides to react with oxygen nitric acid, nitrogen dioxide and NOx subtances
N2(g) +O2(g) —> 2NO(g)
2NO(g) + O2(g) —-> 2NO2(g)
nitrogen dioxide dissolves in rainwater to form acid rain
4NO2(g) + 2H2O(l) +O2(g) —–> 4HNO3(g)
methods to reduce pollution
flue gas deulphurisation
-acidic sulphur dioxide is neutralised by an alkali
-1- mixture of calcium oxide and water is sprayed onto the acidic gas which reacts to make solid calcium sulphate
CaO(s) +2H20(l) +SO2(g) +0.5O2(g) —-> CaSO4(s)
-2-pass the acidic gas through calcium carbonate to produce solid calcium sulphate
CaCO3(s) +0.5O2(l) +SO2(g) —> CaSO4(s)
catalytic converters
in a car and convert some of the harmful gases into less harmful ones
removal of carbon monoxide and nitrogen monoxide
2NO(g) + 2CO(g) —-> N2(g) + 2CO2(g)
removal of unburned hydrocarbons and nitrogen monoxide
C8H18 +25NO —> 8CO2 + 9 H20 + 12.5N2
incomplete combustion of alkanes
limited supplies of oxygen react with alkanes to form carbon monoxide , carbon and water
fraction definition
a mixture of compounds with similar boiling points + similar sized molecules
definition of cracking and the purpose
breaking c-c bonds, high temps and lots of energy to make more useful products
to make alkenes and shorter chain molecules
complete combustion of alkanes
enough oxygen reacts with alkane to form carbon dioxide and water
catalytic cracking
high temp - 720K
slight pressure - around 100KPa , slightly above atmospheric
Zeolite
Gives high abundance of branched alkanes and cycloalkanes