Combustion Notes

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Complete Combustion

Combustion reaction: A chemical reaction where a substance reacts with oxygen, producing heat, light and new products

Complete combustion of a hydrocarbon:

A reaction in which:

Only carbon dioxide and water are produced

Energy is given out

The general equation for complete combustion is:

\(\text{ Hydrocarbon + oxygen}\rightarrow \text{Carbon dioxide + water}\)

Complete combustion occur when there is an excess of oxygen. E.g when the air hole on the Bunsen burner is fully open

An experiment to investigate complete combustion:

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Incomplete Combustion

Incomplete combustion of a hydrocarbon:

A reaction in which:

Water is produced

Less energy is given out than complete combustion

Carbon monoxide and carbon are produced

Incomplete combustion occurs when there is not an excess of oxygen.

What happens to the carbon atoms from the hydrocarbon in a complete combustion reaction?

Some are completely oxidised to carbon dioxide

Some are only partially oxdised to carbon monoxide

Some are released as soot and smoke

Problem with incomplete combustion:

Carbon monoxide is toxic - It combines with haemoglobin in red blood cells and prevents oxygen from being delivered to bodily tissues

Soot can block pipes that carry waste gases away from an appliance

Soot causes breathing problems if it collects in the lungs

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Heat of Combustion

Different organic materials release different amounts of energy when burnt, making them more or less suitable for use as a fuel

Alcohols such as ethanol are often used as fuel. These are not hydrocarbons, as they also contain oxygen, but their combustion has the same product as that of a hydrocarbon.

An experiment to investigate the amount of energy released by a fuel:

\(\text{Heat energy released in a reaction =Mass x Specific heat capacity x change in temperature}\)