Heat of Combustion Calculator

Select a fuel or enter custom enthalpy values to instantly calculate the heat of combustion in kJ/mol, kJ/g, and MJ/kg.

Use the Heat of Combustion Calculator

Combustion Parameters

Heating Value Mode (Water Product State)

Unit Relationships & Scope Limitations

  • 1 kJ/g = 1 MJ/kg: 10³ J / 10⁻³ kg = 10⁶ J/kg. Numerical specific energy and energy density values are identical.
  • HHV vs LHV shift: ΔH°vap(H₂O) = 44.004 kJ/mol at 298.15 K (−241.826 − (−285.830) kJ/mol). Fuels without hydrogen have identical HHV and LHV.
  • Standard reference data: CO₂(g) = −393.5 kJ/mol, H₂O(l) = −285.8 kJ/mol, H₂O(g) = −241.8 kJ/mol (NIST WebBook SRD 69).
  • Combustion scope: Restricted to complete combustion of CₓHᵧOᵤ in pure O₂ yielding CO₂(g) and H₂O. Compounds with positive internal oxygen balance (no O₂ required) are excluded.

Select a fuel and click Calculate to see results.

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Summary

Select a fuel or enter custom enthalpy values to instantly calculate the heat of combustion in kJ/mol, kJ/g, and MJ/kg.

How it works

  1. Choose a preset fuel or select "Custom compound" to provide custom C, H, and O atom counts.
  2. Select either Higher Heating Value (HHV, H₂O liquid) or Lower Heating Value (LHV, H₂O gas).
  3. For custom compounds, enter the standard enthalpy of formation (ΔH°f) in kJ/mol and optional molar mass.
  4. The calculator verifies complete combustion stoichiometry (positive O₂ requirement) and balances the reaction.
  5. It evaluates ΔH°comb = Σ ν_p ΔH°f(products) − Σ ν_r ΔH°f(reactants) using standard NIST enthalpies.
  6. Results display in kJ/mol, kJ/g, and MJ/kg with full step-by-step breakdown and copy actions.

Use cases

  • Compare higher (gross) and lower (net) heating values for hydrocarbons and alcohols.
  • Solve thermochemistry problems in general, physical, and organic chemistry coursework.
  • Calculate theoretical heat releases for boiler, furnace, and engine combustion processes.
  • Verify textbook values for standard molar and mass-specific heats of combustion.
  • Cross-check bomb calorimetry experimental data against theoretical thermodynamic enthalpy.

Frequently Asked Questions

Last updated: 2026-09-23 · Reviewed by Nham Vu