Alkanes. Flashcards
Define petroleum.
Petroleum is a complex MIXTURE of mainly alkane hydrocarbons.
Define a petroleum fraction.
Mixture of hydrocarbons that have similar chain length and boiling point range.
Give all the stages to fractional distillation.
Oil is vaporised (pre heated) and passed into fractionating column.
The fractions will condense at different heights.
The temperature decreases higher up the column.
Separation depends on molecule size which the boiling point is in tern dependent on.
Similar molocules of size boiling point and mass will condense together.
Small condense at the top.
Big condense at the bottom.
What type of process is fractional distillation.
A physical process where weak van Der walls forces are overcome.
What two types of fractional distillation are there.
Lab and industry , don’t confuse the two.
Define the term cracking.
Conversion of large hydrocarbons to smaller hydrocarbon molocules by breaking the C-C.
Give a general equation for cracking.
High Mr alkanes into smaller Mr alkanes +alkenes + (hydrogen sometimes)
State what type of process cracking is and how it is different to the process of fractional distillation.
This is a chemical process as involve the breaking of strong C-C bonds so needs very high temperatures.
Give three economic reasons for cracking
Petroleum fractions with shorter chain lengths like petrol and naphtha are more in demand than those with long chain lengths , to make use of the excess supply of long chain hydrocarbons they are cracked.
The products are more valuable than the starting materials where alkenes ca be used for polymers and branched alkanes can be used for Motor fuels.
Give the conditions for thermal cracking.
High pressure 7000 Kpa and high temp of 700 degrees Celsius.
Give the conditions for catalytic cracking.
A slight pressure not atmospheric. But high temp of 450 degrees Celsius.
Give the products for thermal cracking , give some of their uses.
Produces mostly alkenes where ethene is used for making polymers and also for making ethanol.
Sometimes hydrogen is produced which is used as a starting material in the haber process.
Give the products for catalytic cracking , and the use and why.
Branched cyclic and aromatic hydrocarbons. The branched and cyclic hydrocarbons burn more cleanly and are used to give fuels a higher octane number.
Explain why alkanes can be used as fuels.
They readily burn in oxygen. This is a Highly EXOTHERMIC process.
Define Fuel.
Releases heat energy when it is burnt.
What can be said about the energy released from complete combustion compared to incomplete combustion , compare the products also.
Produces less energy per mole than complete combustion.
Describe overall how the burning of petroleum fractions can lead to acid rain.
Sulphur (not nitrogen) impurities are found in petroleum fractions which produce sulphur dioxide when they are burned. S+O2 into SO2. This sulphur dioxide will dissolve in atmospheric water to produce acid rain , H2SO4.
Give the equation for when CH3SH is combusted.
CH3SH + 3O2 Into SO2 + CO2 + 2H2O
Balance the Hydrogen then the oxygens.
Normal products of complete combustion but add in sulphur.
Describe the process that removes SO2 from the waste gasses from coal fired power-stations , give any equations involved and name the products.
Flue gas desulphurisation.
Flue gasses are waste gasses.
The gases pass through a scrubber containing the basic calcium oxide which will react with the acidic sulphur dioxide in a neutralisation reaction.
SO2 + CaO Into CaSO3 , where the product is Calcium Sulphite.
Give the environmental consequence of NOx componds
. Make distinctions between compounds of Nix in your answer.
NO is a toxic gas and can form NO2 . NO2 is toxic ad acidic and can go on to form acid rain.
