Combustion Reaction Calculator — Hydrocarbon Burning
Enter the carbon and hydrogen atom counts of a hydrocarbon fuel (e.g. octane C₈H₁₈) and the fuel mass in grams. The calculator balances the complete combustion equation and shows exact masses of CO₂, H₂O, and O₂ involved.
g
Mass of carbon dioxide from complete combustion
- 1
Molar mass of fuel
8 × 12.011 + 18 × 1.008 = 114.232 g/mol - 2
Moles of fuel
100 ÷ 114.232 = 0.87541 mol - 3
Moles of CO₂
0.87541 × 16 ÷ 2 = 7.00329 molStoichiometric ratio from the balanced equation. - 4
Mass of CO₂ produced
7.00329 × 44.009 = 308.208 g
Balanced combustion equation
Molar mass of fuel
Moles of fuel
Moles of CO₂
Mass of CO₂
How does this calculator work?
For hydrocarbon CₙHₘ, the balanced combustion equation is CₙHₘ + (n + m/4)O₂ → n CO₂ + (m/2)H₂O. Enter atom counts and fuel mass to get exact grams of CO₂, H₂O, and O₂ via stoichiometric ratios and standard molar masses.
Formula
How this is calculated
Complete combustion of a hydrocarbon CₙHₘ produces only carbon dioxide and water. The unbalanced reaction CₙHₘ + O₂ → CO₂ + H₂O is balanced by applying the rule that each carbon becomes one CO₂ and each pair of hydrogens becomes one H₂O: CₙHₘ + (n + m/4)O₂ → n CO₂ + (m/2)H₂O. To obtain whole-number coefficients, the calculator multiplies all terms by 4 then divides by their greatest common divisor.
The molar mass of the fuel is M = 12.011n + 1.008m g/mol. Dividing the fuel mass by M gives moles of fuel. The stoichiometric ratios from the balanced equation convert moles of fuel to moles of O₂ consumed, CO₂ produced, and H₂O produced. Multiplying by molar masses (O₂ = 31.998, CO₂ = 44.009, H₂O = 18.015 g/mol) converts back to grams.
This calculator models only complete combustion of pure hydrocarbons. Real fuels (petrol, diesel, natural gas) are mixtures; incomplete combustion produces CO and soot. For oxygenated fuels such as ethanol or biodiesel, the formula must be adjusted to account for the oxygen already present in the fuel molecule, which is beyond the scope of this tool.
Frequently asked questions
For CₙHₘ the general balanced equation is CₙHₘ + (n + m/4)O₂ → n CO₂ + (m/2)H₂O. Multiply by 4 to clear fractions, then divide all coefficients by their GCD. Example: CH₄ (methane, n=1, m=4) gives CH₄ + 2O₂ → CO₂ + 2H₂O.
Each carbon atom (mass 12) bonds with two oxygen atoms drawn from the air (mass 32) to form CO₂ (mass 44). The oxygen comes from the atmosphere, not the fuel, so the total mass of CO₂ produced always exceeds the mass of the carbon in the fuel.
Complete combustion (sufficient oxygen) converts all carbon to CO₂ and all hydrogen to H₂O. Incomplete combustion (limited oxygen) produces toxic carbon monoxide (CO) or unburnt carbon soot. This calculator assumes complete combustion only.
Also known as
TG we-Calculate Editorial Team. (2026). Combustion Reaction Calculator — Hydrocarbon Burning [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/combustion-reaction-calculator
TG we-Calculate Editorial Team. "Combustion Reaction Calculator — Hydrocarbon Burning." TG we-Calculate. 2026. https://we-calculate.com/calculator/combustion-reaction-calculator.
TG we-Calculate Editorial Team, "Combustion Reaction Calculator — Hydrocarbon Burning," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/combustion-reaction-calculator
@misc{wecalculate_combustion_reaction_calculator, title = {Combustion Reaction Calculator — Hydrocarbon Burning}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/combustion-reaction-calculator}}, year = {2026}, note = {TG we-Calculate} }
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