What is Heat of combustion?
[[File:Testing White Charcoal Binchotan.JPG|thumb|These pieces of [[charcoal]] have a calorific value of 7543 KCal/kg. They burned for almost 4 hours.]] The '''heat of combustion''', also called '''calorific value''' or '''energy value''' of a [[substance]] is the amount of [[energy]] that is released when burning a given amount of the substance. This energy is released in the form of [[heat]], when the substance is burned in standard conditions. == Chemistry == Heat of combustion (''&Delta;''H''&deg;<sub>c</sub>'') is the measure of the amount of [[energy]] released in the form of [[heat]] (''q'') when one [[mole]] of a substance is burned ([[combustion]]). The production of heat means the [[reaction]] is an [[exothermic]] process and gives off energy. Heat of combustion is a specialized form of reaction [[enthalpy]] because it is measured at [[standard temperature and pressure| standard conditions]] and is limited to one mole starting material. The (&deg;) symbol shows that the heat of combustion value is obtained at standard conditions: 25 degrees Celsius (298.15 [[Kelvin]]) and at a constant pressure. The pressure is reported both at either one [[bar (unit)|bar]] or at one [[atmosphere (unit)|atmosphere]] depending on the source. <ref name=domalski>Domalski, E.S. Selected Values of Heats of Combustion and Heats of Formation of Organic Compounds Containing the Elements C, H, N, O and P. J. Phys. Chem. Ref. Data 1972, 1, pp. 221-277.</ref><ref name=schmidt>Schmidt-Rohr, K. Why Combustions are always exothermic, yielding about 418 kJ per mole of 02. J. Chem. Ed. 2015, 92, 2094-2099.</ref> Heat of combustion is also called the enthalpy of combustion because the energy evolved from the combustion reaction results from the change in the overall enthalpy of the starting substance as it reacts completely with oxygen. The terms heat of combustion and enthalpy of combustion are used interchangeably due to the [[First law of thermodynamics]] and the relationships between heat at constant pressure (''q''<sub>P</sub