Combustion of alkanes
Lajoy Tucker
Teacher
Introduction & Definitions
Combustion: The reaction of a substance with oxygen, releasing heat and light.
Complete Combustion: Occurs when alkanes react fully with excess oxygen to produce carbon dioxide (CO₂) and water (H₂O).
Incomplete Combustion: Occurs when there is a limited supply of oxygen, producing carbon monoxide (CO) or carbon (C, soot) and water.
Basic Principles
Alkanes are used as fuels because they release large amounts of energy on combustion.
These reactions are exothermic.
Examples
A. Complete Combustion
Example with pentane
Word equation:
Pentane + oxygen → carbon dioxide + water
Balanced symbol equation:
B. Incomplete Combustion
Occurs in restricted oxygen supply (e.g. faulty boilers, vehicle engines).
Example with propane (carbon monoxide produced):
Word equation:
Propane + oxygen → carbon monoxide + water
Balanced symbol equation:
Example with butane (carbon/soot produced):
Word equation:
Butane + oxygen → carbon + water
Balanced symbol equation:
Carbon monoxide is toxic, binds to haemoglobin and reduces oxygen transport.
Soot causes breathing problems and global dimming.
No answer provided.
Practice Questions
Question 1
Which product is NOT formed during incomplete combustion of alkanes?
A. Water
B. Carbon monoxide
C. Soot
D. Carbon dioxide
Answer
D. Carbon dioxide
Question 2
Write a balanced equation for the complete combustion of heptane
Answer
Summary
Alkanes burn in excess oxygen (complete combustion) to produce carbon dioxide (CO₂) and water (H₂O).
Alkanes burn in a limited supply of oxygen, producing carbon monoxide (CO) or carbon (C, soot) and water.
Balance combustion equations by balancing C then H then O
No answer provided.