Alkanes - Combustion of Alkanes

Question 1

Why are alkanes used as fuels?

Answer 1

• They release a large amount of energy when they undergo combustion.
• They store a large amount of energy for a small amount of weight.

Question 2

What is combustion?

Answer 2

Reaction between a fuel and oxygen, resulting in the release of energy as heat.

Question 3

What is the difference between complete & incomplete combustion?

Answer 3

• In complete, there is a plentiful supply of oxygen so the fuel reacts completely to form carbon dioxide & water vapour.
• In incomplete, there is an insufficient supply of oxygen so the fuel doesn’t react completely, producing carbon monoxide & water vapour (or solid carbon as soot).

Question 4

Why does incomplete combustion occur? (Example of this happening)

Answer 4

• When there is insufficient oxygen for the fuel to react completely.
• Happens with longer chain alkanes which need more oxygen compared to shorter chains.

Question 5

Why is carbon monoxide harmful?

Answer 5

It is poisonous & can prevent oxygen from binding to haemoglobin in the blood.

Question 6

Explain the low reactivity of alkanes?

Answer 6

• Strong C-C & C-H covalent bonds require a lot of energy to break.
• Non-polar nature of C-C bonds make it difficult for alkanes to attract nucleophiles/electrophiles.