Heat of formation - SEISEINETSU

This refers to the increase in enthalpy when 1 mole of a compound is produced from its constituent elements. Generally, the stable state of these elements at room temperature and normal pressure is chosen as the standard state. For example, the heat of formation at 25°C is expressed as Δ H ° _f,298 . The ° symbol generally indicates the standard state. Since the heat of formation cannot often be calculated as the heat of reaction when directly creating the compound from the elements, in the case of organic compounds, it is calculated by combining the heat of combustion with the heat of formation of _CO2 and _H2O and using Hess's law.

Source: Morikita Publishing "Chemical Dictionary (2nd Edition)" Information about the Chemical Dictionary 2nd Edition

1 mol の化合物がそれを構成する元素から生成されるときのエンタルピー増加をいう．一般に，これら元素は，常温，常圧での安定な状態を標準状態として選ぶ．たとえば，25 ℃ における生成熱はΔ H °_f,298のように表す．°印は一般に標準状態を意味する．生成熱は直接元素からその化合物をつくるときの反応熱として求められない場合が多いから，有機化合物の場合は，その燃焼熱とCO₂およびH₂Oの生成熱を組み合わせ，ヘスの法則を利用して求める．

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