5.1 Cracking Hydrocarbons

Question 1

Describe the 2 ways that cracking can be done

Answer 1

• heating a mixture of hydrocarbon vapours and steam to a very high temperature
• passing hydrocarbon vapours over a hot catalyst

Question 2

Name 2 products of cracking

Answer 2

• alkanes

* alkenes

Question 3

Name 4 features of alkanes

Answer 3

• general formula CnH2n+2
• no double bonds
• saturated
• type of hydrocarbon

Question 4

Give one reason an oil company might want to crack large hydrocarbons to make smaller alkanes

Answer 4

Alkanes with smaller molecules are more useful as fuels

Question 5

What type of reactions produces a mixture of smaller molecules during cracking?

Answer 5

Thermal decomposition

Question 6

Name 4 features of alkenes

Answer 6

• hydrocarbon
• unsaturated
• general formula CnH2n
• double bonds between carbon atoms

Question 7

Why are alkenes unsaturated hydrocarbons?

Answer 7

They contain fewer hydrogen atoms for the same amount of carbon atoms

Question 8

Why are alkenes more reactive than alkanes?

Answer 8

They have a double bond between 2 carbon atoms which are easily broken

Question 9

What is the test for alkenes?

Answer 9

They turn from orange to colourless in bromine water

Question 10

Why do industries often use cracking instead of fractional distillation?

Answer 10

In fractional distillation you get too many unnecessary long hydrocarbons whereas in cracking you can adjust the conditions in order to get the hydrocarbons that you need

Question 11

Give three ways in which alkanes are different from alkenes

Answer 11

• alkenes have double bonds
• have a different general formula
• alkenes have fewer hydrogen atoms
• alkenes are more reactive
• alkenes turn from orange to colourless in bromine water

Question 12

What is cracking?

Answer 12

The process of breaking down longer chained hydrocarbons into short chained hydrocarbons