alkanes

Question 1

unburnt hydrocarbons

Answer 1

are toxic and can cause cancer if breathed in

Question 2

thermal cracking

Answer 2

high temp - 700-1200K
high pressure - 7000KPa
always produce one alkane and all other molecules being alkenes

Question 3

sulphur dioxide - SO2

Answer 3

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

Question 4

process of fractional distillation

Answer 4

-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

Question 5

pollution - chemical produced and polluting effect

Answer 5

CO2 - greenhouse gas
H2O - greenhouse gas
CO - poisonous
Solid C - damages the lungs

Question 6

physical properties of alkanes

Answer 6

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

Question 7

Nitrogenous oxides

Answer 7

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)

Question 8

methods to reduce pollution

Answer 8

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

Question 9

incomplete combustion of alkanes

Answer 9

limited supplies of oxygen react with alkanes to form carbon monoxide , carbon and water

Question 10

fraction definition

Answer 10

a mixture of compounds with similar boiling points + similar sized molecules

Question 11

definition of cracking and the purpose

Answer 11

breaking c-c bonds, high temps and lots of energy to make more useful products

to make alkenes and shorter chain molecules

Question 12

complete combustion of alkanes

Answer 12

enough oxygen reacts with alkane to form carbon dioxide and water

Question 13

catalytic cracking

Answer 13

high temp - 720K
slight pressure - around 100KPa , slightly above atmospheric
Zeolite
Gives high abundance of branched alkanes and cycloalkanes