Combustion Reaction Calculator
Balance complete combustion and calculate oxygen, carbon dioxide, and water amounts.
Complete combustion calculator
Enter a carbon, hydrogen, and optional oxygen fuel formula with its amount.
About complete combustion
A combustion reaction calculator translates a molecular fuel formula into the stoichiometric quantities needed for complete burning. Complete combustion assumes that all carbon atoms become carbon dioxide and all hydrogen atoms become water. For a fuel written in CxHyOz order, one mole produces x moles of carbon dioxide and y divided by two moles of water. The oxygen requirement is x plus y divided by four minus z divided by two. Oxygen already present in an oxygenated fuel therefore reduces the amount supplied from outside.
Balancing matters because atoms are conserved during a chemical reaction. The calculator first counts carbon, hydrogen, and oxygen atoms, then presents coefficients normalized to one mole of fuel. Decimal coefficients are chemically valid and especially useful for material balances. If whole-number coefficients are required for a classroom equation, every coefficient can be multiplied by a common factor. For example, methane uses two oxygen molecules per methane molecule, while propane uses five oxygen molecules and forms three carbon dioxide molecules plus four water molecules.
The amount field scales those coefficients into practical mole quantities. This makes the result useful for introductory stoichiometry, fuel comparison, emission estimates, and preliminary process calculations. The carbon dioxide result is a theoretical maximum for complete combustion; real equipment may also form carbon monoxide, soot, nitrogen oxides, and unburned fuel. Likewise, the water result represents chemically formed water and does not indicate whether it leaves as vapor or liquid.
This tool accepts formulas containing carbon followed by hydrogen and optional oxygen, such as CH4, C3H8, or C2H6O. It does not infer structures, heating values, air composition, conversion efficiency, or incomplete-combustion products. For engineering design, combine the stoichiometric result with excess-air requirements, measured fuel composition, operating conditions, and applicable safety standards. The result is best treated as a transparent mole balance that can be checked directly from conservation of each element.
Combustion examples
| Fuel and amount | Stoichiometric output | Use |
|---|---|---|
| 1 mol CH4 | 2 mol O2, 1 mol CO2, 2 mol H2O | Methane |
| 1 mol C3H8 | 5 mol O2, 3 mol CO2, 4 mol H2O | Propane |
| 1 mol C2H6O | 3 mol O2, 2 mol CO2, 3 mol H2O | Ethanol |
How to calculate a combustion reaction
- Enter the molecular formula with carbon first, hydrogen second, and oxygen last when present.
- Enter the number of moles of fuel being burned.
- Select Calculate combustion to balance the reaction.
- Read the oxygen requirement and theoretical product amounts.
Frequently asked questions
What does complete combustion mean?
Complete combustion converts all fuel carbon to carbon dioxide and all hydrogen to water. It assumes enough oxygen and ideal conversion.
Can this calculator use ethanol?
Yes, enter ethanol as C2H6O. Oxygen within the fuel is included when calculating outside oxygen demand.
Why can an equation have decimal coefficients?
The equation is normalized to one mole of fuel, so half coefficients can appear. Multiply every coefficient by the same factor if whole numbers are preferred.
Does the result include oxygen from air?
The result reports pure oxygen requirement rather than total air. Air calculations must account for oxygen fraction and any desired excess air.
Does it model incomplete combustion?
No, it models ideal complete combustion only. Carbon monoxide, soot, and unburned hydrocarbons require a more detailed model.