Alkanes Flashcards
(13 cards)
Physical Properties of alkanes
• weak vdw
• as it gets longer bp increases
~ more vdw
• branching has lower bp
~ less surface contact
• insoluble in water
~ water is polar
~ non polar don’t dissolve well
Reactivity
Unreactive
C-C is strong
Describe process of Fractional distillation
• Crude oil is heated to vaporise
• Vapour passed in tower
• Which is cooler at top than bottom
• Fractions with low bp/ smallest molecules at top/
fractions separated by bp
Alkanes and saturated
Alkanes are saturated
• Single C-C bond
What factors determine which fraction hydrocarbon separated into
• Bp
• number of C atoms
• strength of vdw
• size/ length
How does volatility determine position of fraction
• most volatile at top
• smallest chain has lowest bp
• thermal energy overcomes intermolecular forces
How is nitrogen oxide formed in engine
• height temps when sparks I fnite fuel
• nitrogen reacts with oxygen
How can sulfur and nitrogen form pollutants
• Nitrogen forms NO2 by reacting with O2
~ at high temps
• N2 + 2O2 —>
What hydrocarbon are more likely to under go incomplete combustion
• longer chains
• Requires more oxygen to burn
Catalytic converters and reduction of pollutants
• Metal coated on honeycomb for large SA
• 2CO + O2 —> 2CO2
• 2CO + 2NO —> 2CO2 + N2
Sulfur dioxide scrubber
• Waste gas passed into scrubbing chamber
• Sprays wet slurry of CaO/ CaCO3
Over it
• clean gases leave chamber
Four products of combustion that have negative effect on human
• CO2
~ deprives body of O2
• CO
~ stops O2 binding to haemoglobin
• C soot or unburnt hydrocarbons
~ inflammation of air ways/ respiratory problems
• NOx and SO2
~ acid rain
Compare two types of cracking
Thermal:
~ High temp, around 1000 K
~ High pressure, 7000 kPa
~ Produces lots of alkenes
~ Forms free radical intermediates
~ Runs for short periods of time to avoid decomposition of products
Catalytic:
~ Low temps, around 720 K
~ Low pressure, 100 kPa
~ Produces branched alkanes
~ Zeolite catalyst
~ Forms carbocation intermediates
