Heat of combustion
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2008-06-15T23:40:32Z
75.72.167.199
/* Lower heating value for some organic compounds (at 25°C) */
The '''heat of combustion''' (ΔH<sub>c</sub><sup>0</sup>) 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 (unit)|mole]] of fuel ([[joule per mole|J/mol]])
* energy/mass of fuel
* energy/volume of fuel
The heat of combustion is traditionally measured with a [[Calorimeter#Bomb calorimeters|bomb calorimeter]]. It may also be calculated as the difference between the [[Standard enthalpy change of formation|heat of formation (Δ<sub>f</sub>''H''<sup>0</sup>)]] of the products and reactants.
== Heating value ==
The '''heating value''' or '''calorific value''' of a [[substance]], usually a [[fuel]] or [[food]], is the amount of [[heat]] released during the combustion of a specified amount of it. The calorific value is a characteristic for each substance.
It is measured in units of [[energy]] per unit of the substance, usually [[mass]], such as: [[calorie|kcal]]/kg, kJ/kg, [[joule|J]]/[[mole (unit)|mol]], [[British thermal unit|Btu]]/m³. Heating value is commonly determined by use of a [[bomb calorimeter]].
The heat of combustion for [[fuel]]s is expressed as the HHV, LHV, or GHV:
* The quantity known as [[higher heating value]] ('''HHV''') (or ''gross calorific value'' or ''gross energy'' or ''upper heating value'') is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. This 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.
* The quantity known as [[lower heating value]] ('''LHV''') (or ''net calorific value'') is determined by subtracting the [[heat of vaporization]] of the water vapor from the higher heating value. This treats any H<sub>2</sub>O formed as a vapor. The energy required to vaporize the water therefore is not realized as heat.
* '''Gross heating value''' (see '''AR''') accounts for water in the exhaust leaving as vapor, and includes liquid water in the fuel prior to combustion. This value is important for fuels like [[wood]] or [[coal]], which will usually contain some amount of water prior to burning.
Most applications which burn fuel produce water vapor which is not used, and thus wasting its heat content. In such applications, the lower heating value is the applicable measure. This is particularly relevant for [[natural gas]], whose high [[hydrogen]] content produces much water. The gross calorific value is relevant for gas burnt in [[condensing boiler]]s which condense the water vapor produced by combustion, recovering heat which would otherwise be wasted.
Both HHV and LHV can be expressed in terms of AR (all moisture counted), MF and MAF (only water from combustion of hydrogen). AR, MF, and MAF are commonly used for indicating the heating values of coal:
* '''AR''' (As Received) indicates that the fuel heating value has been measured with all moisture and ash forming minerals present.
* '''MF''' (Moisture Free) or '''Dry''' indicates that the fuel heating value has been measured after the fuel has been dried of all inherent moisture but still retaining its ash forming minerals.
* '''MAF''' (Moisture and Ash Free) or '''DAF''' (Dry and Ash Free) indicates that the fuel heating value has been measured in the absence of inherent moisture and ash forming minerals.
== Heat of combustion for common fuels (higher value) ==
{| class="wikitable"
|-
! colspan="4" | Heat of Combustion
|-
! Fuel
! [[Joule|MJ]]/[[kilogram|kg]]
! [[calorie|Mcal]]/[[kilogram|kg]]
! [[BTU]]/[[pound (mass)|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
|}
== Lower heating value for some organic compounds (at 25°C) ==
{| class="wikitable"
|-
! Fuel
! [[megajoule|MJ]]/[[kilogram|kg]]
! [[megajoule|MJ]]/[[liter|L]]
! [[BTU]]/[[pound (mass)|lb]]
! [[Joule|kJ]]/[[mole (unit)|mol]]
|-
! colspan="5" | Paraffins
|-
| [[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
| —
| —
| —
|-
|-
! colspan="5" | Isoparaffins
|-
| [[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
| -
| —
| —
|-
! colspan="5" | Naphthenes
|-
| [[Cyclopentane]]
| 44.636
| —
| —
| —
|-
| [[Methylcyclopentane]]
| 44.636
| —
| —
| —
|-
| [[Cyclohexane]]
| 43.450
| —
| —
| —
|-
| [[Methylcyclohexane]]
| 43.380
| —
| —
| —
|-
! colspan="5" | Monoolefins
|-
| [[Ethylene]]
| 47.195
| —
| —
| —
|-
| [[Propylene]]
| 45.799
| —
| —
| —
|-
| [[1-Butene]]
| 45.334
| —
| —
| —
|-
| [[cis-2-Butene]]
| 45.194
| —
| —
| —
|-
| [[trans-2-Butene]]
| 45.124
| —
| —
| —
|-
| [[Isobutene]]
| 45.055
| —
| —
| —
|-
| [[1-Pentene]]
| 45.031
| —
| —
| —
|-
| [[2-Methyl-1-pentene]]
| 44.799
| —
| —
| —
|-
| [[1-Hexene]]
| 44.426
| —
| —
| —
|-
! colspan="5" | Diolefins
|-
| [[1,3-Butadiene]]
| 44.613
| —
| —
| —
|-
| [[Isoprene]]
| 44.078
| -
| —
| —
|-
! colspan="5" | Nitrous derivated
|-
| [[Nitromethane]]
| 10.513
| —
| —
| —
|-
| [[Nitropropane]]
| 20.693
| —
| —
| —
|-
! colspan="5" | Acetylenes
|-
| [[Acetylene]]
| 48.241
| —
| —
| —
|-
| [[Methylacetylene]]
| 46.194
| —
| —
| —
|-
| [[1-Butyne]]
| 45.590
| —
| —
| —
|-
| [[1-Pentyne]]
| 45.217
| —
| —
| —
|-
! colspan="5" | 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
| —
| —
| —
|-
! colspan="5" | 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
| —
| —
| —
|-
! colspan="5" | Ethers
|-
| [[Methoxymethane]]
| 28.703
| —
| —
| —
|-
| [[Ethoxyethane]]
| 33.867
| —
| —
| —
|-
| [[Propoxypropane]]
| 36.355
| —
| —
| —
|-
| [[Butoxybutane]]
| 37.798
| —
| —
| —
|-
! colspan="5" | Aldehydes and ketones
|-
| [[Methanal]]
| 17.259
| —
| —
| —
|-
| [[Ethanal]]
| 24.156
| —
| —
| —
|-
| [[Propionaldehyde]]
| 28.889
| —
| —
| —
|-
| [[Butyraldehyde]]
| 31.610
| —
| —
| —
|-
| [[Acetone]]
| 28.548
| —
| —
| —
|-
! colspan="5" | Other species
|-
| [[Graphite|Carbon (graphite)]]
| 32.808
| —
| —
| —
|-
| [[Hydrogen]]
| 120.971
| —
| —
| —
|-
| [[Carbon monoxide]]
| 10.112
| —
| —
| —
|-
| [[Ammonia]]
| 18.646
| —
| —
| —
|-
| [[Sulfur]] (<small>solid</small>)
| 9.163
| —
| —
| —
|-
|}
Note that there is no difference between the lower and higher heating values for the combustion of carbon, carbon monoxide and sulfur since no water is formed in combusting those substances.
== Heating values of some fuels ==
{|class=wikitable align=left
|+Higher (HHV) and Lower (LHV) Heating values<BR>of some common fuels<ref name=NIST>[http://webbook.nist.gov/chemistry NIST Chemistry WebBook]</ref>
! Fuel !! HHV [[Joule|MJ]]/[[kilogram|kg]] !! HHV [[BTU]]/[[pound (mass)|lb]] !! HHV [[Joule|kJ]]/[[mole (unit)|mol]] !! LHV [[MJ/kg]]
|-
| [[Hydrogen]]|| 141.8 || 61,100 || 286 || 121
|-
| [[Methane]] || 55.5 || 23,900 || 889 || 50.0
|-
| [[Ethane]] || 51.9 || 22,400 || 1570 || 47.8
|-
| [[Propane]]|| 50.35 || 21,700 || 2220 || 46.35
|-
| [[Butane]]|| 49.5 || 20,900 || 2875 || 45.75
|-
| [[Pentane]]|| || || || 45.35
|-
| [[Gasoline]] || 47.3 || 20,400 || || 44.4
|-
| [[Paraffin]] || 46 || 19,900 || 16,300
|-
| [[Kerosene]] || 46.2 || || || 43.0
|-
| [[Diesel]] || 44.8 || 19,300 || ||
|-
| [[Coal]] || 15–27 || 8000–14,000 || 200–350 ||
|-
| [[Wood]]|| 15 || 6500 || 300 ||
|-
| [[Peat]]|| 6–15 || 2500–6500 || ||
|}
{|class=wikitable align=center
|+Higher heating value<BR> of less common fuels<ref name=NIST/>
! Fuel !! HHV [[Joule|MJ]]/[[kilogram|kg]] !! [[BTU]]/[[pound (mass)|lb]] !! [[Joule|kJ]]/[[mole (unit)|mol]]
|-
| [[Methanol]] || 22.7 || 9800 || 726
|-
| [[Ethanol]] || 29.7 || 12,800 || 1300
|-
| [[Propanol]]|| 33.6 || 14,500 || 2020
|-
| [[Acetylene]]|| 49.9 || 21,500 || 1300
|-
| [[Benzene]] || 41.8 || 18,000 || 3270
|-
| [[Ammonia]] || 22.5 || 9690 || 382
|-
| [[Hydrazine]] || 19.4 || 8370 || 622
|-
| [[Hexamine]]|| 30.0 || 12,900 || 4200
|-
| [[Carbon]] || 32.8 || 14,100 || 393.5
|}
{{clear}}
== Higher heating values of natural gases from various sources ==
These data on higher heating values were obtained from the International Energy Agency:<ref name=KWES>[http://iea.org/dbtw-wpd/Textbase/nppdf/free/2005/key2005.pdf Key World Energy Statistics (2005), page 59]</ref>
* [[Russia]]: 38,231 kJ/m³
* [[United States]]: 38,416 kJ/m³
* [[Canada]]: 38,200 kJ/m³
* [[Netherlands]]: 33,320 kJ/m³
* [[United Kingdom]]: 39,710 kJ/m³
* [[Indonesia]]: 40,600 kJ/m³
* [[Algeria]]: 42,000 kJ/m³
* [[Uzbekistan]]: 37,889 kJ/m³
* [[Saudi Arabia]]: 38,000 kJ/m³
* [[Norway]]: 39,877 kJ/m³
* [[Bangladesh]]: 36,000 kJ/m³
The lower heating values of the above natural gases are about 90 percent of the higher heating values.
== Fuel needed to run a 100 W lightbulb for a year (876 kWh, or 3153.6 MJ) ==
(The fuel quantities below assume 100% conversion efficiency. As most power generation/distribution systems only achieve 30% - 35% efficiency, the actual quantity of fuel used to power a 100 W light bulb in your home will be about three times the quantity shown.)
* 117 to 210 kg (257 to 462 lb) of coal (using the heating values in the table above)
* 73.34 kg (161.6 lb) of kerosene
* 78.8m³, of natural gas, using an average value of 40000 kJ/m³.
*.006 kg (.014 lb) of uranium
* 17.5 µg (0.000000039 lb) of [[antimatter]]
== References ==
{{reflist}}
* "Carburants et moteurs", J-C Guibet, Publication de l'Institut Français du Pétrole, ISBN 2-7108-0704-1
== See also ==
* [[Adiabatic flame temperature]]
* [[Combustion]]
* [[Energy density]]
* [[Energy value of coal]]
* [[Exothermic reaction]]
* [[Fire]]
* [[Fuel efficiency#Energy content of fuel]]
* [[Food energy]]
* [[Internal energy]]
* [[Thermal efficiency]]
* [[Wobbe index]]: heat density
== External links ==
* [http://webbook.nist.gov/chemistry/ NIST Chemistry WebBook]
* [http://www.wendellhull.com ASTM Standard Testing]
[[Category:Chemical engineering]]
[[Category:Combustion]]
[[Category:Energy]]
[[Category:Fuels]]
[[Category:Heat]]
[[Category:Nuclear physics]]
[[Category:Thermochemistry]]
[[Category:Thermodynamic properties]]
[[Category:Thermodynamics]]
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