cracking & alkenes

Question 1

why can hydrocarbons be cracked?

Answer 1

to produce smaller, more useful molecules

Question 2

two methods of cracking

Answer 2

-steam
-catalytic

Question 3

cracking definition

Answer 3

a reaction in which larger saturated hydrocarbon molecules are broken down into smaller more useful hydrocarbon molecules

Question 4

what do the products of cracking include?

Answer 4

alkanes and alkenes

Question 5

catalytic cracking conditions, what happens, what are products, how are products separated?

Answer 5

-heat at 550°C until they vaporise into a gas
-passed over a hot, powdered zeolite catalyst (aluminium oxide and silicon oxide)
-shorter chain alkanes and an alkene
-fractional distillation

Question 6

steam cracking conditions, what happens, how are products separated?

Answer 6

-800°C
-70 atm
-no catalyst
-long chain of hydrocarbon turned into a gas then mixed with steam
-alkenes separated from alkanes by fractional distillation

Question 7

alkenes v alkanes which is more reactive?

Answer 7

alkenes

Question 8

why are alkenes produced?

Answer 8

there aren’t enough carbon atoms to make two alkanes

Question 9

alkenes

Answer 9

unsaturated hydrocarbon

Question 10

why are alkenes more reactive?

Answer 10

they have a double bond

Question 11

describe the test for alkenes

Answer 11

-add alkenes to bromine water
-if it turns colourless, alkenes are present
-if it stays orange, there are no alkenes

Question 12

what are the products of cracking useful as and why?

Answer 12

fuels - there is a high demand for fuels with small molecules

Question 13

uses of alkenes

Answer 13

produce polymers and as starting materials for
the production of many other chemicals