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The entropy of fusion is the increase in entropy when melting a substance. This is almost always positive since the degree of disorder increases in the transition from an organized crystalline solid to the disorganized structure of a liquid; the only known exception is helium. It is denoted as ΔSfus and normally expressed in J mol−1 K−1 A natural process such as a phase transition will occur when the associated change in the Gibbs free energy is negative. :, where is the enthalpy or heat of fusion. Since this is a thermodynamic equation, the symbol T refers to the absolute thermodynamic temperature, measured in Kelvin (K). Equilibrium occurs when the temperature is equal to the melting point so that :, and the entropy of fusion is the heat of fusion divided by the melting point. : ==Helium== Helium-3 has a negative entropy of fusion at temperatures below 0.3 K. Helium-4 also has a very slightly negative entropy of fusion below 0.8 K. This means that, at appropriate constant pressures, these substances freeze with the addition of heat. 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「entropy of fusion」の詳細全文を読む スポンサード リンク
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