Heat of combustion

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The Heat of combustion (Δ_cH⁰) is the energy released as heat when a compound undergoes complete combustion with oxygen. The chemical reaction is typically a hydrocarbon reacting with oxygen to form carbon dioxide, water and heat. It may be expressed with the quantities:

• energy/mole of fuel
• energy/mass of fuel
• energy/volume of fuel

The heat of combustion is traditionally measured with a bomb calorimeter. It may also be calculated as the difference between the heat of formation (Δ_fH⁰) of the products and reactants.

Contents 1 Heating value 2 Heat of combustion for common fuels (higher value) 3 Lower heating value for some organic compounds (at 25°C) 4 Reference 5 See also 6 External links

[edit] Heating value

The heat of combustion for fuels is expressed as the HHV (Higher Heating value) or LHV (Lower Heating Value).

Lower heating value treats any H₂O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat.

Higher Heating Value is the same as the thermodynamic heat of combustion since the enthalpy change for the reaction assumes a common temperature of the compounds before and after combustion, in which case the water produced by combustion is liquid.

[edit] Heat of combustion for common fuels (higher value)

Heat of Combustion
Fuel	MJ/kg	Mcal/kg	BTU/lb
Hydrogen	141.9	33.9	61,000
Gasoline	47	11.3	20,400
Diesel	45	10.7	19,300
Ethanol	29.8	7.1	12,800
Propane	49.9	11.9	21,500
Butane	49.2	11.8	21,200
Wood	15	3.6	6,500
Coal	15-27	4.4 - 7.8	8,000 - 14,000
Natural Gas	~54	~13	~23,000

[edit] Lower heating value for some organic compounds (at 25°C)

Fuel	MJ/kg	kJ/L	BTU/lb	kJ/mol
Paraffines
Methane	50.009	---	---	---
Ethane	47.794	---	---	---
Propane	46.357	---	---	---
Butane	45.752	---	---	---
Pentane	45.357	---	---	---
Hexane	44.752	---	---	---
Heptane	44.566	---	---	---
Octane	44.427	---	---	---
Nonane	44.311	---	---	---
Decane	44.240	---	---	---
Undecane	44.194	---	---	---
Dodecane	44.147	---	---	---
Isoparaffines
Isobutane	45.613	---	---	---
Isopentane	45.241	---	---	---
2-Methylpentane	44.682	---	---	---
2,3-Dimethylbutane	44.659	---	---	---
2,3-Dimethylpentane	44.496	---	---	---
2,2,4-Trimethylpentane	44.310	---	---	---
Naphtene
Cyclopentane	44.636	---	---	---
Methylcyclopentane	44.636	---	---	---
Cyclohexane	43.450	---	---	---
Methylcyclohexane	43.380	---	---	---
Olefines
Ethylene	47.195	---	---	---
Propylene	45.799	---	---	---
But-1-ene	45.334	---	---	---
(Z)-But-2-ene	45.194	---	---	---
(E)-But-2-ene	45.124	---	---	---
Isobutene	45.055	---	---	---
Pent-1-ene	45.031	---	---	---
2-Methylpent-1-ène	44.799	---	---	---
Hex-1-ene	44.426	---	---	---
Diolefines
Buta-1,3-diene	44.613	---	---	---
Isoprene	44.078	---	---	---
Nitrous derivated
Nitromethane	10.513	---	---	---
Nitropropane	20.693	---	---	---
Acetylenics
Acetylene	48.241	---	---	---
Methylacetylene	46.194	---	---	---
But-1-yne	45.590	---	---	---
Pent-1-yne	45.217	---	---	---
Aromatics
Benzene	40.170	---	---	---
Toluene	40.589	---	---	---
o-Xylene	40.961	---	---	---
m-Xylene	40.961	---	---	---
p-Xylene	40.798	---	---	---
Ethylbenzene	40.938	---	---	---
1,2,4-Trimethylbenzene	40.984	---	---	---
Propylbenzene	41.193	---	---	---
Cumene	41.217	---	---	---
Alcohols
Methanol	19.937	---	---	---
Ethanol	28.865	---	---	---
n-propanol	30.680	---	---	---
Isopropanol	30.447	---	---	---
n-Butanol	33.075	---	---	---
Isobutanol	32.959	---	---	---
Tertiobutanol	32.587	---	---	---
n-Pentanol	34.727	---	---	---
Ethers
Methoxymethane	28.703	---	---	---
Ethoxyethane	33.867	---	---	---
Propoxypropane	36.355	---	---	---
Butoxybutane	37.798	---	---	---
Aldehydes and ketones
Methanal	17.259	---	---	---
Ethanal	24.156	---	---	---
Propionaldehyde	28.889	---	---	---
Butyraldehyde	31.610	---	---	---
Acetone	28.548	---	---	---
Other species
Carbon (graphite)	32.808	---	---	---
Hydrogen	120.971	---	---	---
Carbon monoxide	10.112	---	---	---
Ammonia	18.646	---	---	---
Sulfur	4.639	---	---	---

[edit] Reference

• "Carburants et moteurs", J-C Guibet, Publication de l'Institut Français du Pétrole, ISBN 2-7108-0704-1

[edit] See also

• Energy density
• Combustion
• Exothermic reaction
• Fire
• Internal energy

[edit] External links

• NIST Chemistry WebBook
• ASTM Standard Testing