大学物理双语-热力学基础.pptVIP

* * * Chapter 12 Thermodynamics Chapter 12 Thermodynamics The First Law of Thermodynamics The application of First Law of Thermodynamics Cyclic process and Carnot circulation The 2nd Law of Thermodynamics and Entropy The First Law of Thermodynamics 热力学第一定理 Quasi-steady process (准静态过程) : p1,V1 p2,V2 Quasi-steady process is also called as equilibrium process (平衡过程). F=pS dl dA=Fdl=pSdl=pdV The work done by the gas : When the piston is moved slowly and change the volume of gas from V1 to V2 , the total work done by the gas is: ò ò = = . 2 1 V V pdV dA A Quasi-steady process and work (1) It is the shaded area under the p-V process curve between initial to final state 功是过程曲线下的面积. (2) The work done by the gas depends on the process 功与过程有关,功是过程量. Descriptions: (3) The work done by the gas is positive when its volume expands;otherwise, negative. Experimentally, it is found that both work A and heat Q are dependent on the nature of the process. However, a surprising thing is that the quantity Q - A is the same for all processes between two states . It depends only on the initial and final states. Q – A= Constant The first law of thermodynamics (Q - A的改变只取决于初、末两个状态，与所经历的过程无关) Quantity Q - A represents intrinsic property of the thermodynamic system. This intrinsic property is called the internal energy ?E, which is a function of state, or a state-function (内能是状态的单值函数). So The First Law of Thermodynamics. For a differential process, it can be written as: It is hold for any system and any process. The first law of thermodynamics “系统从外界吸收的热量,一部分使系统的内能增加,另一部分用于对外做功”. About the sign of Ａ, Q, and E: work done by the system dＡ 0 system absorbs heat dQ 0 system’s energy increasing dE 0 ??能量守恒定律 (第一类永动机??不需能量输入而能继续做功的机器??不存在） Physical meaning: The first law of thermodynamics 2. The application of First Law of Thermodynamics 热力学第一定理的应用 1. Constant-volume process (等体过程) 2. Constant-pressure process (等压过程) 3. Constant-temperature process (等温