Cracking Flashcards

1
Q

what is cracking

A

turning long saturated (alkane) molecules into smaller unsaturated (alkenes) and alkane molecules

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2
Q

what is cracking a form of and what is the definition of that

A
  • its a form of thermal decomposition

- which is when one substance breaks down into two or more substances when you heat it

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3
Q

what does thermal decomposition consist of and what is used to counteract this

A
  • it means breaking strong covelant bonds
  • so you need lots of energy
  • catalysts are often used to speed the reactions up
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4
Q

why are the longer hydrocarbons produced from fractional distillation cracked into smaller hydrocarbons

A
  • because there is more of a demand for products such as petrol and diesel
  • rather than bitumen and fuel oil
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5
Q

what can alkanes produced from cracking alternatively be used for

A

it can be used for making polymers (mostly plastic)

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6
Q

what is done during the cracking of hydrocarbons

A
  • vaporised hydrocarbons are passed over powdered catalysts at a temp of 400 to 700C at 70atm
  • the long chain molecules split apart or crack on the surface of the bits of catalyst
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7
Q

what catalyst is used for cracking hydrocarbons

A

aluminium oxide

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8
Q

how can you crack hydrocarbons in a lab

A
  • heat alkane until its vaporised
  • pass it through a tube with powdered aluminium oxide at the bottom, in the middle
  • hydrocarbons break down when it comes into contact with catalyst
  • producing a mixture of short chain alkanes and alkenes
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9
Q

you can be given a table which shows fraction of hydrocarbon, the percentage of crude oil they have and the percentage in demand. What would the typical display on this table

A
  • shorter hydrocarbons like gases and petrol would have a higher demand than what is produced
  • the longer hydrocarbons like bitumen or fuel oil would have a higher production percentage than the demand
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10
Q

if the question linked to the table asks you which fraction is more likely to be cracked to provide us with petrol and diesel oil, what would be the typical responses (kerosene and bitumen and fuel oil are above demand)

A
  • crack kerosene fraction to supply the extra petrol
  • and crack the bitumen and fuel oil fraction to supply the extra diesel oik
  • OR, crack the fuel oil and bitumen to supply the extra petrol and diesel oil
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