# 3.22: Combustion Reactions

Difficulty Level: At Grade Created by: CK-12
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Don’t try this at home! This performer isn’t really eating fire, but he still puts on an impressive show. You know that fire is dangerous. It’s hot, it can burn you, and it can easily get out of control. But do you know what fire is? Fire is the result of a chemical reaction. Whenever something burns, a type of reaction called a combustion reaction occurs.

### What Is a Combustion Reaction?

A combustion reaction occurs when a substance reacts quickly with oxygen (O2). For example, in the Figure below, charcoal is combining with oxygen. Combustion is commonly called burning, and the substance that burns is usually referred to as fuel. The products of a complete combustion reaction include carbon dioxide (CO2) and water vapor (H2O). The reaction typically gives off heat and light as well. The general equation for a complete combustion reaction is:

Fuel + O2 → CO2 + H2O

The burning of charcoal is a combustion reaction.

### Combustion of Hydrocarbons

The fuel that burns in a combustion reaction contains compounds called hydrocarbons. Hydrocarbons are compounds that contain only carbon (C) and hydrogen (H). The charcoal pictured above consists of hydrocarbons. So do fossil fuels such as natural gas. Natural gas is a fuel that is commonly used in home furnaces and gas stoves. The main component of natural gas is the hydrocarbon called methane (CH4). You can see a methane flame in the Figure below. The combustion of methane is represented by the equation:

CH4 + 2O2 → CO2 + 2H2O

The combustion of methane gas heats a pot on a stove.

Q: Sometimes the flame on a gas stove isn’t just blue but has some yellow or orange in it. Why might this occur?

A: If the flame isn’t just blue, the methane isn’t getting enough oxygen to burn completely, leaving some of the carbon unburned. The flame will also not be as hot as a completely blue flame for the same reason.

You can simulate the combustion of hydrocarbons, including methane, at this URL: http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/stoichiometry/stoic_excess_oxy.html

### Summary

• A complete combustion reaction occurs when a fuel reacts quickly with oxygen (O2) and produces carbon dioxide (CO2) and water (H2O). The general equation for a complete combustion reaction is: Fuel + O2 → CO2 + H2O
• The fuel that burns in a combustion reaction usually consists of hydrocarbons, which contain only carbon (C) and hydrogen (H). An example of a hydrocarbon is methane (CH4), the main component of natural gas.

### Vocabulary

• combustion reaction: Chemical reaction in which a substance reacts quickly with oxygen, producing carbon dioxide, water, and energy; commonly called burning.

### Practice

Watch the video about combustion reactions at the following URL, and then answer the questions below.

1. When does complete combustion occur? What are the products of complete combustion?
2. When does incomplete combustion occur? What are the products of incomplete combustion?

### Review

1. What is a combustion reaction?
2. Write the general equation for a combustion reaction.
3. When iron rusts, it slowly combines with oxygen to form iron oxide. Is rusting a combustion reaction?

### Notes/Highlights Having trouble? Report an issue.

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### Vocabulary Language: English

TermDefinition
combustion reaction Chemical reaction in which a substance reacts quickly with oxygen, producing carbon dioxide, water, and energy; commonly called burning.

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