Combustion Reaction Calculator
Balance the complete combustion of a compound containing carbon, hydrogen, and oxygen, then verify atom conservation at a glance.
Fuel composition
Required nonnegative integer.
Required nonnegative integer.
Use 0 for a hydrocarbon.
Balanced result
Smallest whole-number coefficients
CH₄ + 2 O₂ → CO₂ + 2 H₂O
Fuel coefficient
1
CO₂ coefficient
1
H₂O coefficient
2
Atom-balance check
| Element | Reactant atoms | Product atoms | Difference |
|---|
How to use the combustion reaction calculator
What this calculator does
This calculator balances the ideal, complete combustion of a single compound whose molecular formula contains only carbon, hydrogen, and oxygen. It determines the smallest whole-number stoichiometric coefficients for the fuel, oxygen, carbon dioxide, and water. It is useful for checking homework, preparing a stoichiometric calculation, or confirming a reaction before a larger mass or mole balance. It does not predict flame temperature, heat release, reaction rate, excess-air requirements, pollutant formation, or incomplete-combustion products such as carbon monoxide and soot.
When to use it
Use it when you need to balance the complete combustion of a hydrocarbon such as methane, propane, or hexane; an oxygenated fuel such as ethanol; or another C-H-O compound. It is also helpful when checking whether a proposed equation conserves each element, converting fractional coefficients into the simplest integer ratio, or creating a reproducible workbook for a laboratory note or class assignment. The underlying balancing rule follows conservation of matter, explained in this guide to coefficients, subscripts, and balanced equations.
How to calculate
- Enter the number of carbon atoms in Total atoms of carbon C (α).
- Enter the hydrogen count in Total atoms of hydrogen H (β).
- Enter the oxygen count in Total atoms of oxygen O (γ); use zero for a hydrocarbon.
- Read the live Smallest whole-number coefficients equation and the three coefficient cards.
- Check the Atom-balance check table. Every Difference entry should be zero.
- Select Download Excel to export the current inputs, coefficients, equation, and atom check as a validated .xlsx workbook. Select Reset to restore the methane example C₁H₄O₀.
Input guide
Total atoms of carbon C (α) is a required nonnegative whole number. Enter digits only, for example 3 for propane, C₃H₈. Increasing carbon raises the carbon-dioxide coefficient and generally increases oxygen demand. Do not enter a molar mass, decimal, chemical symbol, or coefficient. Total atoms of hydrogen H (β) is also a required nonnegative integer; 8 is a realistic propane value. More hydrogen increases water production and oxygen demand. An odd hydrogen count is allowed, because the calculator scales the complete equation to whole numbers. Total atoms of oxygen O (γ) is a required nonnegative integer; enter 0 for methane or 1 for ethanol, C₂H₆O. Oxygen already present in the fuel reduces the external O₂ requirement. A formula that would require zero or negative external oxygen is outside this calculator's complete-combustion-with-O₂ scope and is rejected visibly.
Output guide
Fuel shows the constructed molecular formula. O₂ coefficient is the integer oxygen coefficient in the simplified equation. Whole-number form confirms that fractional coefficients were scaled away. Smallest whole-number coefficients is the primary balanced identity. The Fuel coefficient, CO₂ coefficient, and H₂O coefficient cards show the stoichiometric mole ratio. These are exact balancing coefficients, not experimental yields. In the Atom-balance check, Reactant atoms and Product atoms are independently counted from the displayed coefficients; Difference must equal zero for C, H, and O. A high coefficient is not inherently inefficient – it often results from simplifying a fractional ratio.
Worked example
For methane, enter carbon 1, hydrogen 4, and oxygen 0. The unsimplified relationships are b = α = 1 for CO₂, c = β/2 = 2 for H₂O, and a = α + β/4 – γ/2 = 1 + 4/4 – 0 = 2 for O₂. All values are already integers, so the smallest balanced equation is CH₄ + 2 O₂ → CO₂ + 2 H₂O. The atom table reports 1 carbon atom, 4 hydrogen atoms, and 4 oxygen atoms on each side, with zero difference in every row. For context on real-world products beyond this idealized model, see the U.S. EPA overview of combustion products and indoor air quality.
How the balancing formula works
For a fuel written CαHβOγ, complete combustion is represented as CαHβOγ + aO₂ → bCO₂ + cH₂O. Carbon balance gives b = α. Hydrogen balance gives c = β/2. Oxygen balance then gives a = α + β/4 – γ/2. Because chemical equations are normally reported as the smallest whole-number ratio, the calculator converts these rational values into integers and divides all coefficients by their greatest common divisor.
Integer basis: fuel = 4, O₂ = 4α + β – 2γ, CO₂ = 4α, H₂O = 2β; then divide all four numbers by their greatest common divisor.
The integer-basis form avoids floating-point rounding and makes parity exact for integer molecular subscripts. It also reveals the required domain condition: 4α + β – 2γ must be positive when molecular oxygen is a reactant. Complete combustion of C-H-O materials ideally forms carbon dioxide and water; the EPA notes that materials composed only of carbon, hydrogen, and oxygen form those products under complete-combustion conditions in its discussion of combustion products from C-H-O materials.
Assumptions and common mistakes
The model assumes complete, stoichiometric combustion with pure O₂ shown explicitly. Real systems usually use air, may operate with excess oxygen, and can form carbon monoxide, unburned hydrocarbons, nitrogen oxides, soot, or other products. The calculator does not add atmospheric nitrogen or estimate emissions. For environmental context, the EPA explains that carbon dioxide is released by burning fossil fuels and other carbon-containing materials in its overview of greenhouse gases.
Do not alter subscripts to balance an equation; subscripts define the substance itself. Change only coefficients in front of formulas. Do not reduce only one side of the equation, and do not assume a decimal coefficient is wrong – multiply every coefficient by the same factor, then reduce the full set. Finally, remember that stoichiometric coefficients describe mole or molecule ratios, not equal masses. A separate molar-mass calculation is required to convert those ratios to grams.