Combustion reactions
All hydrocarbons (including alkanes, alkenes and cycloalkanes) can undergo combustion reactions with oxygen to give the same two products. Hydrocarbon fuels burn when they react with oxygen in the air. As all hydrocarbons only contain the elements carbon and hydrogen, the only products will be oxides of these elements. So as long as enough oxygen is present for complete combustion, the two products formed will be carbon dioxide (CO2) and water (H2O). The word equation for this reaction is shown below.
\(hydrocarbon + oxygen \to carbon\,dioxide + water\)
The products from the combustion of hydrocarbon fuels can be identified with the following set up in the lab.
Watch this demonstation of identifying the products of combustion of hydrocarbons
Carbon dioxide gas turns limewater from colourless to milky white. In the above experiment, the limewater in the boiling tube changes colour indicating carbon dioxide is produced by combustion of the hydrocarbon fuel.
If water is produced it will condense in the U-tube cooled by the ice water. This results in cobalt chloride paper changing the colour from blue to pink.
Incomplete combustion (when there is an insufficient supply of oxygen) could lead to toxic carbon monoxide (CO) being produced instead of carbon dioxide.
This video shows a demonstration of two types of chemical reaction, one which gives out heat energy and one which takes in heat energy.