You need a substance and then that substance has to have a property that changes depending on the heat flow, i.e., depending on whether it's sensing that it's the same temperature or different temperature than something else.

你需要某种物质,它的某种性质,随着热量的流动而改变，也就是说,依赖于它是否感觉到它,与其他的物体处于相同的温度。

麻省理工公开课 - 热力学与动力学课程节选

It's just how much heat is involved when we change the temperature. Now, the products have some heat capacity associated with them right, it takes a certain amount of heat if we make their temperature change, to either put it in or take it away, depending on which direction the temperature is changing.

问题就是当我们改变温度时,有多少热量发生了转移,生成物具有一定的热容,如果我们改变,它们的温度，就要输入或,提取一定的热量,这取决于温度改变的方向。

麻省理工公开课 - 热力学与动力学课程节选