Combustion Reactions

The synthesis reaction between sulfur dioxide and oxygen can be classified also as a combustion reaction. In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light. Oxygen can combine in this way with many different substances, making combustion reactions common.

A combustion reaction, such as the one shown in Figure 10-6, occurs between hydrogen and oxygen when hydrogen is heated. Water is formed during the reaction and a large amount of energy is released.

Figure 10-6 The tragedy of the Challenger space mission was the result of a combustion reaction between

Another important combustion reaction occurs when coal is burned to produce energy. Coal is called a fossil fuel because it contains the remains of plants that lived long ago. It is composed primarily of the element carbon. Coal-burning power plants generate electric power in many parts of the United States. The primary reaction that occurs in these plants is between carbon and oxygen.

C(s) + O₂(g) ® CO₂(g)

Note that the combustion reactions just mentioned are also synthesis reactions. However, not all combustion reactions are synthesis reactions. For example, the reaction involving methane gas, CH₄, and oxygen illustrates a combustion reaction in which one substance replaces another in the formation of products.

CH₄(g) + 2O₂(g) ® CO₂(g) + 2H₂O(g)

Methane, which belongs to a group of substances called hydrocarbons, is the major component of natural gas. All hydrocarbons contain carbon and hydrogen and burn in oxygen to yield the same products as methane does—carbon dioxide and water. For example, most cars and trucks are powered by gasoline, which contains hydrocarbons. In engines, gasoline is combined with oxygen, producing carbon dioxide, water, and energy that powers the vehicles.

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