Thermal equilibrium

Japanese: 熱平衡 - ねつへいこう（英語表記）thermal equilibrium

When a system of objects capable of exchanging heat is in thermal equilibrium, and there is no transfer of heat between them and no change in phase, the system is said to be in thermal equilibrium, and the temperature of each object in thermal equilibrium is equal. In general, an isolated system will always reach thermal equilibrium if left alone for a long enough time. If A and B are in thermal equilibrium, and A and C are also in thermal equilibrium, then when B and C are placed in direct thermal contact, they will always be in thermal equilibrium. This fact is called the zeroth law of thermodynamics. This is why the quantity temperature can be assigned to each state of thermal equilibrium. In addition, A, which acts as an intermediary to determine whether or not thermal equilibrium is achieved when B and C are in direct thermal contact, can be thought of as a thermometer. In addition to stable states, thermal equilibrium can also include metastable states such as overheating and supersaturation. Whether a system is in thermal equilibrium under various conditions can be determined by the maximum or minimum of an appropriate thermodynamic function.

Source: Encyclopaedia Britannica Concise Encyclopedia About Encyclopaedia Britannica Concise Encyclopedia Information

Japanese:

熱の交換が可能な物体系において，物体間に熱の移動がなく，かつ相の変化もないときに，これらの物体系は熱平衡にあるといい，熱平衡にある各物体の温度は等しい。一般に孤立した系は十分に長く放置すれば必ず熱平衡の状態になる。AとBが熱平衡にあり，AとCも熱平衡にあれば，BとCとを熱的に直接接触させると必ず熱平衡にある。この事実を熱力学第零法則という。これが温度という量をそれぞれの熱平衡状態に与えることができる理由である。またBとCを熱的に直接接触させたときに熱平衡であるかどうかを，介在して判定するAは温度計とみなせる。熱平衡状態には安定状態のほかに過熱や過飽和のような準安定状態もある。種々の条件のもとで系が熱平衡状態にあることの判定は，適当な熱力学的関数の極大または極小によって与えられる。

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