Alkanes Flashcards
(12 cards)
What type of hydrocarbons are alkanes?
- saturated hydrocarbons
- obtained from fractional distillation of petroleum/crude oil
What is cracking
Converting long, less useful alkanes into smaller, more useful alkanes
It involves breaking the C-C bond
Types of cracking
Thermal and catalytic
Thermal cracking
Conditions
High temp (700-1200K), high pressure (7MPa)
products
High proportions of alkenes
intermediates involved
Free radicals
Catalytic cracking
conditions
High temp (700K)
Slight pressure (1-2 atm)
Zeolite catalyst
products
Aromatic hydrocarbons
Branched hydrocarbons eg used for motor fuels
Economic benefits of cracking
Smaller hydrocarbons are more useful as fuels=supply of fuels is improved=helps match supply w demand
Fractional distillation
Properties of alkanes
Longer chains=stronger vdW forces=higher boiling point
Straight chain=pack more closely tgt=more interaction bw electron clouds=stronger vdW forces=more energy require to break them
Combustion of alkanes
complete combustion=CO2 released=greenhouse gas=global warming
incomplete combustion
CO=silent killer=binds w Hb in rbc=less oxygen reaches ur body cells
C particulates=blackens buildings+global dimming
SO2=reacts with water to form H2SO4=acid rain=damages vegetation (sulfur impurities)
NOx=reacts w water to form HNO3=acid rain=damages vegetation
Unburned hydrocarbons=wastes fuel+harmful+a greenhouse gas
Flue gas desulfurisation
w calcium oxide
Calcium oxide+water=calcium sulfite (further oxidised=gypsum/calcium sulfate=sold to make builders’ plaster+plasterboard
CaO (s)+2H2O (l)+SO2 (g)+0.5O2 —> CaSO4.2H2O (s)
w calcium carbonate/limestone
CaCO3 (s)+0.5O2 (g)+SO2 (g) —> CaSO4 (s)+CO2 (g)
Catalytic converters
Installed on vehicle exhaust systems to remove pollutants.
Contain a honeycomb structure coated with catalyst metals such as platinum, rhodium, and palladium.
These metals catalyse the conversion of harmful compounds into less harmful substances as exhaust gases pass through.
They oxidise carbon, carbon monoxide, and unburnt hydrocarbons into carbon dioxide and water, while reducing nitrogen oxides to nitrogen and oxygen gases
Free radical substitution
Initiation
UV light chlorine gas molecules beak homolytically=form chlorine free radicals
propagation
- chlorine free radical reacts w a methane molecule=stripping a H atom forming HCl+methyl free radical=reacts w another chlorine molecule=regenerates another chlorine free radical (self-propagating reactions)
termination
2 free radical species react to form a stable molecule
