Then the second derivative gives the change in entropy with respect to the variable that we're differentiating, with respect to which is either pressure or volume.

二阶导数给出熵,随着变量变化的情况，这些变量包括压强或者体积。

麻省理工公开课 - 热力学与动力学课程节选

In general, the second law gave us the Clausius inequality for spontaneous change.

一般来说第二定律给出了,自发变化的克劳修斯不等式。

麻省理工公开课 - 热力学与动力学课程节选