3.2- alkanes Flashcards
(25 cards)
what is crude oil
-mixture of hydrocarbons, mainly alkanes
stages of fractional distillation (4)
- crude oil heated until vapourised
- vapour passed into fractionating column- hot at bottom, cool at top
- different fractions condense at different levels due to different BPs
4.fractions are pumped away separately
what are fractions
compounds/mixtures with a similar BP/carbon chain length
why do short chain alkanes have lower BPs than long chain alkanes
weaker VDW forces between molecules so less energy needed to overcome forces
what is fractional distillation (2)
-used to separate crude oil- alkanes have different BPs so the mixture can be separated
-its a physical process-no bonds are broken
properties of smaller chain molecules (5)
-short chain alkanes
-low BP
-very volatile
-flows easily
-ignites easily
what is cracking (3)
-thermal decomposition reaction
-breaking a C-C bond in large molecules (eg. alkanes) to give smaller molecules (eg. alkenes and branched alkanes)
-chemical process- covalent bonds are broken
thermal cracking: conditions, products, use of products
-high temp (≈1000°C), high pressure
-produces alkenes and some short chain alkanes
-products used to make polymers (plastics)
catalytic cracking: conditions, products, use of products
-low pressure, high temp (≈450°C), zeolite catalyst
-produces branched chain alkanes, cycloalkanes and aromatic hydrocarbons
-products used as motor fuel
why are shorter chain alkanes more useful
more useful as they are in higher demand therefore more money is made
complete combustion equation
hydrocarbon+oxygen->carbon dioxide+water
incomplete combustion equation
hydrocarbon+oxygen->carbon monoxide/carbon+water
what is sulfur dioxide (2)
-produced during combustion
-environmental problem- when combined with water and air it forms sulfuric acid->acid rain
what is flue gas desulfurisation (3)
-used in power stations to remove sulfur dioxide from flue gases- reduces acid rain
-flue gases are reacted with calcium oxide
-sulfur reacts with calcium oxide to form sulfite salts (CaCO3)
what 3 pollutants do petrol engines produce
-carbon monoxide and carbon
-nitrogen oxides (NO and NO2)
-unburned hydrocarbons
why is carbon monoxide a pollution problem + how is it formed
-affects amount of greenhouse gases
-incomplete combustion: hydrocarbon+O2->CO+H2O
why is carbon a pollution problem + how is it formed
-traps heat in atmosphere, leading to global warming
-incomplete combustion: hydrocarbon+O2->C+H2O
why is nitrogen monoxide a pollution problem
reacts with other pollutants to form smog which damages plants and lungs
which 3 catalysts are used in catalytic converters
platinum
palladium
rhodeum
Name a laboratory technique that could be used to separate isooctane from a mixture of octane and isooctane.
Outline how this technique separates isooctane from octane. (3)
fractional distillation
isooctane has a lower BP so it’ll condense first
isooctane condenses and is collected
CO is produced when incomplete combustion takes place in engines. NO is another pollutant produced in car engines.
Write an equation to show how these pollutants react together in a catalytic converter.
2CO + 2NO → 2CO2 + N2
why is a thin layer of the catalysts in catalytic converters used
to reduce amount of metals needed whilst producing a large surface area
how is nitrogen monoxide formed
formed from N2 reacting with O2 at high temp in pressure engines
why does CO2 absorb infrared radiation
-has polar bonds
