Activation Energy Calculator
Calculate activation energy using the Arrhenius equation with two-temperature rate data. Supports Ea from rate constants, frequency factor estimation, and temperature dependence analysis.
Combustion Reaction Calculator
Calculate heat released, oxygen required, and products formed in combustion reactions. Supports hydrocarbons, alcohols, and custom organic fuels with complete/incomplete combustion.
Common Fuels
0 for hydrocarbons
g
2C₍8₎H₍18₎ + 25O₂ → 16CO₂ + 18H₂O
Molar Mass of Fuel⧉
114.23 g/mol
C8H18
O₂ Required⧉
350.2 g
10.943 mol = 0.25 L at STP
CO₂ Produced⧉
308.2 g
7.003 mol = 0.16 L at STP
H₂O Produced⧉
141.9 g
7.879 mol
Air Required⧉
1,509.3 g
Air/Fuel ratio: 15.09:1 by mass
Energy Released⧉
4,789.4 kJ
47,894 kJ/kg = 11,447 kcal/kg
CO₂ Emission Factor⧉
3.082 g/g fuel
3,082.1 g CO₂ per kg fuel
Fuel Comparison Table
| Fuel | Formula | ΔH°c (kJ/mol) | kJ/g | g CO₂/g fuel | Air/Fuel |
|---|---|---|---|---|---|
| Methane (CH₄) | C1H4 | -890 | 55.5 | 2.744 | 17.2 |
| Ethane (C₂H₆) | C2H6 | -1560 | 51.9 | 2.927 | 16.1 |
| Propane (C₃H₈) | C3H8 | -2220 | 50.3 | 2.994 | 15.6 |
| Butane (C₄H₁₀) | C4H10 | -2878 | 49.5 | 3.029 | 15.4 |
| Octane (C₈H₁₈) | C8H18 | -5471 | 47.9 | 3.082 | 15.1 |
| Methanol (CH₃OH) | C1H4O1 | -726 | 22.7 | 1.374 | 6.5 |
| Ethanol (C₂H₅OH) | C2H6O1 | -1367 | 29.7 | 1.911 | 9.0 |
| Acetylene (C₂H₂) | C2H2 | -1300 | 49.9 | 3.380 | 13.2 |
| Benzene (C₆H₆) | C6H6 | -3268 | 41.8 | 3.381 | 13.2 |
| Glucose (C₆H₁₂O₆) | C6H12O6 | -2803 | 15.6 | 1.466 | 4.6 |
Energy Density Comparison
Methane
55.5 kJ/g
Ethane
51.9 kJ/g
Propane
50.3 kJ/g
Butane
49.5 kJ/g
Octane
47.9 kJ/g
Methanol
22.7 kJ/g
Ethanol
29.7 kJ/g
Acetylene
49.9 kJ/g
Benzene
41.8 kJ/g
Glucose
15.6 kJ/g
Planning notes, formulas, and examples
About the Combustion Reaction Calculator
Combustion reactions are exothermic chemical reactions in which a fuel reacts with oxygen to produce heat, carbon dioxide, and water. They are the basis of energy production from fossil fuels, internal combustion engines, power plants, and even cellular respiration (in a biochemical sense). Understanding combustion stoichiometry is essential for engineering, environmental science, and chemistry.
For a generic hydrocarbon CₓHᵧ, the balanced equation is: CₓHᵧ + (x + y/4)O₂ → xCO₂ + (y/2)H₂O. When oxygen-containing fuels like alcohols are burned, the equation adjusts to account for the oxygen already present in the fuel molecule. This calculator handles hydrocarbons, alcohols, and general CₓHᵧOᵤ compounds.
This calculator computes the balanced equation, moles of O₂ required, volumes of CO₂ and H₂O produced, heat released (using standard enthalpies), air-fuel ratio, and CO₂ emission factor. It helps engineers size combustion chambers, environmental scientists estimate emissions, and students practice stoichiometry.
When This Page Helps
Balancing combustion equations and computing stoichiometric quantities by hand is tedious for complex fuels. This calculator quickly provides the balanced equation, mass/volume relationships, energy output, and emission factors.
How to Use the Inputs
- Enter the number of carbon, hydrogen, and oxygen atoms in your fuel molecule.
- Or select a common fuel from the presets (methane, propane, octane, etc.).
- Enter the mass or moles of fuel to be burned.
- Select complete or incomplete combustion mode.
- Review the balanced equation, O₂ requirement, and products.
- Check the energy output and CO₂ emissions.
- Compare different fuels using the reference table.
Formula used
Balanced combustion: CₓHᵧOᵤ + (x + y/4 - z/2)O₂ → xCO₂ + (y/2)H₂O
Heat released ≈ ΔH°c (from standard tables or estimated)
Air/Fuel ratio (mass) = mass O₂ required × (100/23.2) / mass fuel
CO₂ emission = x × 44.01 / molar mass of fuel (g CO₂ per g fuel)Example Calculation
Result: Balanced: 2C₈H₁₈ + 25O₂ → 16CO₂ + 18H₂O
Octane (C₈H₁₈) requires 12.5 mol O₂ per mol fuel. For 100 g octane (0.877 mol), this means 10.96 mol O₂ = 350.6 g O₂. Complete combustion produces 7.02 mol CO₂ (308.8 g) and 7.89 mol H₂O (142.2 g), releasing approximately 4,817 kJ.
Tips & Best Practices
- Complete combustion requires a lean (excess air) mixture; most burners use 10-20% excess air.
- The stoichiometric air-fuel ratio for gasoline is about 14.7:1 by mass.
- CO₂ emission factors are used to estimate greenhouse gas inventories.
- Incomplete combustion wastes fuel energy and produces toxic CO — ensure adequate ventilation.
- Oxygenated fuels (alcohols, ethers) require less external O₂ because they contain oxygen.
- Natural gas (mostly CH₄) produces the least CO₂ per unit energy among fossil fuels.
Combustion Stoichiometry Basics
Every combustion calculation starts with a balanced chemical equation. For hydrocarbons CₓHᵧ, the general equation is CₓHᵧ + (x + y/4)O₂ → xCO₂ + (y/2)H₂O. The coefficients tell us the exact mole ratios, from which mass ratios and volume ratios (for gases at STP) follow directly.
Energy from Combustion
The heat released in combustion (ΔH°c) depends on the bonds broken and formed. Breaking C –H and C–C bonds requires energy; forming C=O (in CO₂) and O–H (in H₂O) bonds releases energy. The net result is always exothermic for hydrocarbons. Standard enthalpies of combustion are tabulated for hundreds of compounds.
Environmental Impact
Combustion of fossil fuels is the primary source of anthropogenic CO₂ emissions. The carbon intensity of a fuel — grams CO₂ per megajoule of energy — varies: natural gas (56 g/MJ) < gasoline (69 g/MJ) < coal (92 g/MJ). Switching from coal to natural gas reduces CO₂ emissions by about 40% per unit energy.
Sources & Methodology
Last updated:
Frequently Asked Questions
Complete combustion occurs when sufficient oxygen is available, producing only CO₂ and H₂O. Incomplete combustion produces CO, soot (C), or other partially oxidized products.
The O₂ requirement depends on the fuel formula. For CₓHᵧ hydrocarbons: (x + y/4) moles O₂ per mole of fuel.
The stoichiometric air-fuel ratio is the exact mass of air needed per unit mass of fuel for complete combustion. Air is about 23.2% oxygen by mass.
When oxygen supply is limited, carbon is only partially oxidized to CO instead of CO₂. This releases less energy and produces toxic carbon monoxide gas.
Hydrogen has the highest energy per unit mass (~142 MJ/kg), but gaseous hydrogen has low volumetric energy density. Among liquid fuels, gasoline (~46 MJ/kg) and diesel (~45 MJ/kg) are the most energy-dense.
CO₂ emissions = moles of carbon × 44.01 g/mol CO₂. Higher carbon content fuels produce more CO₂ per unit energy.
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