熵

表征系统无序性的大小

\begin{array}{r} S \propto \ln Ω \end{array}

\begin{aligned} S & = k \ln Ω \end{aligned}

$k$ 为玻尔兹曼常数

\begin{array}{r} Δ S = S_{2} - S_{1} = k (\ln Ω_{2} - \ln Ω_{1}) = k \ln (\frac{Ω_{2}}{Ω_{1}}) \end{array}

\begin{array}{r} Ω (V, T) = Ω_{p} Ω_{v} \end{array}