Combustion Reaction Calculator
Balance complete combustion reactions and calculate O₂ needed + CO₂/H₂O produced. Enter a fuel (like C₃H₈ or C₂H₆O) and this calculator builds: Fuel + O₂ → CO₂ + H₂O with clean steps and optional amounts (moles / grams).
Background
In complete combustion, all carbon becomes CO₂ and all hydrogen becomes H₂O. If the fuel contains oxygen, it reduces how much O₂ you need.
How to use this calculator
- Choose a calculator mode: balance only or amounts.
- Enter a fuel using a chemical formula (e.g. C₃H₈) or atom counts.
- In Amounts mode, enter fuel moles or grams.
- Optionally enable limiting reagent / excess O₂ and enter available oxygen.
- Click Calculate to see the balanced equation, moles, grams, and CO₂ volume at STP.
How this calculator works
- Parse the fuel into atom counts C, H, O.
- Set CO₂ coefficient = C and H₂O coefficient = H/2.
- Balance oxygen using (2C + H/2 − O)/2.
- Clear fractions to obtain integer coefficients.
- In Amounts mode, convert moles → grams and CO₂ → liters at STP.
Formula & Equations Used
Combustion: Fuel + O₂ → CO₂ + H₂O
O₂ required: (2C + H/2 − O)/2
STP volume: V = n × 22.414 L/mol
Example Problems & Step-by-Step Solutions
Example 1 — Propane combustion
Balance the combustion of C₃H₈.
- CO₂ = 3, H₂O = 4
- O₂ = 5
- C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O
Example 2 — Mass of CO₂ produced
How many grams of CO₂ are produced when 2.0 mol of propane combust completely?
- From the balanced equation: 1 mol C₃H₈ → 3 mol CO₂
- 2.0 × 3 = 6.0 mol CO₂
- Molar mass of CO₂ = 44.01 g/mol
- 6.0 × 44.01 ≈ 264 g CO₂
Example 3 — CO₂ volume at STP
Find the volume of CO₂ at STP produced from 1.5 mol of CO₂.
- Use molar volume at STP: 22.414 L/mol
- V = 1.5 × 22.414 ≈ 33.6 L
Frequently Asked Questions
Does this calculator support incomplete combustion?
No. It assumes complete combustion only.
Why do I sometimes see fractions?
Fractions appear before coefficients are scaled to whole numbers.
