Chemistry / Unit 7: Chemical Reactions
7.6 Combustion Reactions
Notes
In a combustion reaction, a substance reacts rapidly with oxygen, releasing heat and light.
- Hydrocarbons (C and H compounds) burn completely to form $\text{CO}_2$ and $\text{H}_2\text{O}$.
- Balance C first, then H, then O last.
- Example: $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$.
- Propane: $\text{C}_3\text{H}_8 + 5\text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$.
- If O comes out odd, double everything: $2\text{C}_2\text{H}_6 + 7\text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$.
- With too little oxygen, incomplete combustion makes toxic carbon monoxide (CO).
Practice
What are the products of the complete combustion of butane, $\text{C}_4\text{H}_{10}$?
Complete combustion of any hydrocarbon makes carbon dioxide and water.
What coefficient goes in front of $\text{O}_2$ when $\text{C}_3\text{H}_8 + \_\ \text{O}_2 \rightarrow 3\text{CO}_2 + 4\text{H}_2\text{O}$ is balanced?
Products have $3(2) + 4(1) = 10$ O atoms, so 5 $\text{O}_2$ are needed.
What is the coefficient of $\text{O}_2$ in the balanced equation $2\text{C}_2\text{H}_6 + \_\ \text{O}_2 \rightarrow 4\text{CO}_2 + 6\text{H}_2\text{O}$?
Products have $4(2) + 6(1) = 14$ O atoms, so $7\text{O}_2$.
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