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The heat of combustion is the energy released as heat when a compound undergoes complete combustion with oxygen under standard conditions. 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 (kJ/mol) * energy/mass of fuel * energy/volume of the fuel The heat of combustion is conventionally measured with a bomb calorimeter. It may also be calculated as the difference between the heat of formation of the products and reactants. The heating value (or energy value or calorific value) of a substance, usually a fuel or food (see food energy), is the amount of heat released during the combustion of a specified amount of it. The energy value is a characteristic for each substance. It is measured in units of energy per unit of the substance, usually mass, such as: kJ/kg, kJ/mol, kcal/kg, Btu/lb. Heating value is commonly determined by use of a bomb calorimeter. Heating value unit conversions: * kcal/kg = MJ/kg * 238.846 * Btu/lb = kJ/kg * 2.3238 * Btu/lb = kcals/kg * 1.8 The heat of combustion for fuels is expressed as the HHV, LHV, or GHV. == Higher heating value == The quantity known as higher heating value (HHV) (or ''gross energy'' or ''upper heating value'' or ''gross calorific value'' (GCV) or ''higher calorific value'' (HCV)) is determined by bringing all the products of combustion back to the original pre-combustion temperature, and in particular condensing any vapor produced. Such measurements often use a standard temperature of . 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 higher heating value takes into account the latent heat of vaporization of water in the combustion products, and is useful in calculating heating values for fuels where condensation of the reaction products is practical (e.g., in a gas-fired boiler used for space heat). In other words, HHV assumes all the water component is in liquid state at the end of combustion (in product of combustion) and that heat below can be put to use. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Heat of combustion」の詳細全文を読む スポンサード リンク
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