4.7.1.3 Properties of hydrocarbons

Question 1

What do the properties of some hydrocarbons depend on?

Answer 1

• The size of the molecules

Question 2

What do the properties boiling point, viscosity, and flammability influence?

Answer 2

• How hydrocarbons are used as fuels

Question 3

How does boiling point change with increasing molecular size (chain length)?

Answer 3

• The boiling point increases as the chain length increases
• At room temperature:
  
  • short chain length = gas
  • medium chain length = liquid
  • large chain length = solid

Question 4

How does viscosity change with increasing molecular size (chain length)?

Answer 4

• The viscosity increases as the chain length increases
  
  • short chain length = more volatile
    (evaporate more quickly) as low boiling
    pt
  • large chain length = more viscos (more
    thick and sticky)

Question 5

How does flammability change with increasing molecular size (chain length)?

Answer 5

• The flammability decreases as the chain length increases
  
  • short chain length = burn easier
  • long chain length = takes longer to
    burn

Question 6

What does the combustion of hydrocarbon fuels release?

Answer 6

• Energy (hydrocarbons main use is as fuels, release lots of energy when burned with oxygen)

Question 7

What happens to the hydrocarbons during combustion?

Answer 7

• The carbon and hydrogen in the fuels are oxidised
• Complete combustion of hydrocarbon produces carbon dioxide and water

Question 8

What is complete combustion?

Answer 8

• When there is enough oxygen to react with the hydrocarbon
• Produces carbon dioxide and water
• Releases a lot of energy, an exothermic reaction

Question 9

What is the general formula for complete combustion?

Answer 9

• Hydrocarbon + oxygen = carbon dioxide + water
• CH + “oxidized” = OCO (CO2) + HOH (H2O)

Question 10

Write the balanced equation for the complete combustion of propane.

Answer 10

C3H8 + O2 = CO2 + H2O

balanced = C3H8 + 5O2 = 3CO2 + 4H2O

Question 11

Write the balanced equation for the combustion of nonane.
- Nonane (C9H20)

Answer 11

C9H20 + O2 = CO2 + H2O

balanced = C9H20 + 14O2 9CO2 + 10H2O