Combustion Examples in Chemistry

Start with the recap, study the fully worked examples, then use the practice problems to check your understanding of Combustion.

This page combines explanation, solved examples, and follow-up practice so you can move from recognition to confident problem-solving in Chemistry.

Concept Recap

A rapid exothermic reaction between a fuel and oxygen, producing carbon dioxide and water (for hydrocarbon fuels).

Burning. When something burns, it's reacting with oxygen and releasing energy as heat and light.

Read the full concept explanation →

How to Use These Examples

  • Read the first worked example with the solution open so the structure is clear.
  • Try the practice problems before revealing each solution.
  • Use the related concepts and background knowledge badges if you feel stuck.

What to Focus On

Core idea: Complete combustion of hydrocarbons produces CO₂ and H₂O. Incomplete combustion produces CO (toxic) and soot.

Common stuck point: Combustion always requires oxygen. Without enough O₂, incomplete combustion produces carbon monoxide (dangerous).

Worked Examples

Example 1

easy
Write the balanced equation for the complete combustion of ethanol (\text{C}_2\text{H}_5\text{OH}).

Solution

  1. 1
    Complete combustion of a hydrocarbon/alcohol produces \text{CO}_2 and \text{H}_2\text{O}.
  2. 2
    Unbalanced: \text{C}_2\text{H}_5\text{OH} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.
  3. 3
    Balance C: 2 \text{CO}_2. Balance H: 6 H atoms → 3 \text{H}_2\text{O}. Balance O: products have 2(2) + 3(1) = 7 O. Reactant has 1 O in ethanol, so need 6 more from \text{O}_2 → 3 \text{O}_2.
  4. 4
    \text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}.

Answer

\text{C}_2\text{H}_5\text{OH} + 3\text{O}_2 \rightarrow 2\text{CO}_2 + 3\text{H}_2\text{O}
Combustion reactions are always exothermic. Complete combustion requires sufficient oxygen and produces only \text{CO}_2 and \text{H}_2\text{O}. Incomplete combustion produces CO or soot (C).

Example 2

medium
What is the difference between complete and incomplete combustion of methane (\text{CH}_4)? Write equations for both.

Practice Problems

Try these problems on your own first, then open the solution to compare your method.

Example 1

easy
Balance the combustion of butane: \text{C}_4\text{H}_{10} + \text{O}_2 \rightarrow \text{CO}_2 + \text{H}_2\text{O}.

Example 2

hard
Ethanol (\text{C}_2\text{H}_5\text{OH}) is used as a fuel additive. Write the balanced equation for its complete combustion. If only limited oxygen is available, what products form instead (incomplete combustion)?
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Background Knowledge

These ideas may be useful before you work through the harder examples.

chemical reactionexothermic