5.1自发过程的方向性 The Direction of Spontaneous Process 5.2热力学第二定律的表述 Statement of the Second Law of Thermodynamics 5.3卡诺循环与卡诺定律 Carnot cycle and Carnot Theorem 5.4熵、熵增原理及熵方程 Entropy, The increase principle of Entropy and Entropy Equation 5.5熵的意义及应用 Significance of Entropy and its application