(O) Topic 12 - Alkanes
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State the characteristics of a homologus series (3 points)
• Same general formula • trend in physical properties • similar chemical properties
What are saturated hydrocarbons?
Molecules containing no C=C and Hydrogen and Carbon Only
Describe: Trend in boiling points in alkanes
the longer the carbon chain, the stronger van der waal’s forces between molecules. (more branched chains = lower bp)
Describe how fractional distillation work?
Crude oil is vaporised and passed into a tower which is hot at the bottom and cool at the top. As the vapour rises, different compounds with different boiling points condense at different heights, being filtered off and seperated. The smaller the molecule the lower the boiling point
What comes out of each fraction (top to bottom)
• Fuel Gases • Gasoline • Naphtha • Kerosene • Diesel • Residue
What is cracking?
When surplus larger hydrocarbon chains in low demand are broken up into demand shorter hydrocarbon chains.
What are the conditions for thermal cracking?
900 degrees C 70 atm Products - Alkenes
What are the conditions for catalytic cracking
450 degrees C 1-2 atm catalyst - zeolites products - motor fuels (aromatics, cyclic alkanes and branched alkanes)
What is reforming and why is it done?
When straight chain hydrocarbons are converted to branched or cylic alkanes, as they are burnt more efficiently and used in petrol for cars
Pollutants from burning fossil fuels (there are 6)
• CO2 • CO • C (soot) • SO2 • NOx (NO2 or NO) • unburned Hydrocarbons
What is the issue with SO2 and NOx? How can they be dealt with?
Acid rain: - SO2 - Flue Gas Desulfurisation - NOx - Catalytic Converters
Describe Flue Gas Desulfurisation and write the equations.
The gases pass trhough a scrubber containing calcium oxide or calcium carbonate which reacts with the SO2 CaO + SO2 -> CaSO3 or CaCO3 + SO2 -> CaSO3 + CO2 This is an acid base reactions and the product can be used to make plasterboard.
Describe Catalytic Converters and write the equation
Catalytic converters remove CO, NO, NO2 and unbured hydrocarbons by passing them over a ceramic honeycomb coated with a catalyst (Pt, Pd or Rh) 2CO + 2NO -> 2CO2 + N2
Explain Global Warming
Greenhouse gases absorb IR radiation given off by the earth. They contain polar bonds and as they absorb IR these bonds vibrate, warming the earth.
What are the 3 stages of free radical substitution?
Initiation Propogation Termination
To Practice
Free Radical Substitution Mechanism