Combustion, or burning, is the reaction of a chemical with oxygen to produce oxides and energy.

When organic compounds undergo combustion, certain chemical products and large quantities of energy will be produced. The exact nature of the chemicals produced by the combustion reaction will depend on the amount of available oxygen and the composition of the fuel being combusted. In general, two types of combustion occur  -  complete combustion and incomplete combustion.

1. Complete Combustion
   
   Complete combustion involves a fuel reacting with excess oxygen to produce carbon dioxide and water vapour. In the complete combustion of a hydrocarbon, only two chemical compounds are formed. Energy is produced also.
   
    
   
   
   Hydrocarbon derivatives also can undergo complete combustion. For example, methanol can be used as a fuel.
   
   
   
   
   Methanol is considered a clean-burning fuel because, similar to a hydrocarbon, the only products of its complete combustion are carbon dioxide, water vapour, and energy.
   
   Many fuels are not as clean burning as methanol. For example, gasoline may be contaminated with sulfur. When sulfur undergoes complete combustion, sulfur dioxide is produced. This is a very undesirable product because it reduces air quality and can result in acid deposition (such as acid rain).

   
   

   In Canada, a federal mandate requires the reduction of sulfur in gasoline. Refineries in Alberta have upgraded their equipment to reduce sulfur content in their products.

   
   
   
2. Incomplete Combustion
   
   Incomplete combustion of a hydrocarbon or hydrocarbon derivative occurs when the supply of oxygen is limited. During incomplete combustion, various products are possible, including C (carbon - known as soot), carbon monoxide, carbon dioxide, and water vapour. The respective amounts of these products depend primarily on the proportion of oxygen available.
   
   Hydrocarbon + (insufficient) O₂(g) → xC(s) + y CO(g) + zCO₂(g) + H₂O(g) + energy
   
   C(s) is soot and carbon monoxide (CO) is a toxic gas that can reach dangerous levels in confined areas.

Carbon dioxide is a product of both complete and incomplete combustion. An excess of carbon dioxide gas in the atmosphere can cause significant problems.

Watch the following animation for a simplified view of the problem. What solutions are being proposed to reduce the amount of carbon dioxide in our atmosphere?

Check Your Understanding

Complete Practice Question 1 on page 399 of the textbook.

Check your work by clicking on the link beneath.