Alkanes Flashcards
What does fractional distillation of crude oil do?
Separate hydrocarbons into fractions
What two physical processes are involved in fractional distillation
Boiling and condensation (as fractions leave column as liquids)
What is a fraction
A mixture of hydrocarbons with similar boiling points
What do C1 to C4 carbons make
Liquefied petroleum gas
What do C5 to C9 carbons make
Chemicals
What do C5 to C10 carbons make
Petrol for vehicles
What do C10 to C16 carbons make
Jet fuel and paraffin
What do C14 to C20 carbons make
Diesel fuels
What do C20 to C50 carbons make
Waxes, lubricants and polishes
What do C20 to C70 carbons make
Fuels for ships, factories and central heating
What do >C70 carbons make
Bitumen for roads and roofing
Describe fractional distillation
Hydrocarbons separates due to different boiling points
Boiling point depends on C Chain length
Cooler at top of column
Higher boiling point chains evaporated at the bottom of the column
Define saturated hydrocarbons
Contains single bonds ONLY
Define unsaturated
Contains at least one C=C double bond
Define hydrocarbon
Contains hydrogen and carbon only
Why do we crack long chain alkanes?
Shorter chain alkanes are in higher demand
Give the conditions of thermal cracking
High temperature- 1000K
High pressure- 7000kPa
Free radical intermediates
What does thermal cracking produce
High percentage of alkenes and straight chain alkanes
Give the conditions of catalytic cracking
High temperature- 720K
Moderate pressure - 100-500kPa
Uses catalysts eg zeolite crystals
Carbocations intermediates
What is catalytic cracking used to produce
Motor fuels
Aromatic hydrocarbons
Cycloalkanes
What are the products of the complete combustion of alkanes
H20 and CO2
Products of the incomplete combustion of hydrocarbons
CO and water
Or
C and water
Why is
a) carbon monoxide
b) Carbon particulates
c) CO2
a pollutant
a) It is poisonous
b) exacerbates asthma
c) green house gas
Why are Nitrogen oxides Sulphur dioxide Water vapour Pollutants?
NO and NO2 form nitric acid with water and cause acid rain
SO2 forms H2SO4, causing acid rain
Water vapour is a greenhouse gas
How is NO and NO2 formed
N2 and O2 react together when a spark is generated in a hot engine
How is sulphur removed?
Give the equation
Glue gas desulphurisation:
It is neutralised by CaO or CaCO3
CaO + SO2 —> CaSO3
This prevents acid rain
Why is CaO used in desulphurisation
It is a base and SO2 is acidic
Why are catalytic converters fitted to cars
Reduce amount of CO, C, and NO produces
Equation for formation of NO
N2 + O2 —> NO2
Describe the catalyst used in catalytic converters
Honeycomb structure to increase surface area and improve cost effectiveness
Made of ceramic material to withstand high temperatures
Honeycomb is coated in catalyst (eg Platinum, palladium or rhodium)
What happens to the pollutant gases as they pass over the catalyst in a converter?
They are adsorbed on the surface of the catalyst (held to the catalyst’s surface)
What is the equation for the conversion of CO and NO in a catalytic converter
2CO + 2NO —> 2CO2 + N2
What is the equation for C8H18 and NO in a catalytic converter?
C8H18 + 25NO —> 8CO2 + 12.5N2 +9H2O
Conditions for catalytic cracking
What does it produce
High temperature
Moderate pressure
Zeolite catalyst
Branched and cyclic alkanes,
Aromatics
Motor fuels
How is the exhaust gas octane removed
React with NO in a catalytic converter to produce CO2, N2 and H2O
Reaction of octane and NO
C8H18 + NO —-> CO2 + N2 + H2O
