UNIVERSITY PHYSICS I CHAPTER 15 The Second law of Thermodynamics and Entropy Chapter 15 The second law of thermodynamics The zeroth law of thermodynamics The expression of the fundamental experiment fact The first law of thermodynamics The a statement of conservation of energy for pure thermodynamic system The second law of thermodynamics: Why we need the second law of thermodynamics?
1 Chapter 15 The second law of thermodynamics The zeroth law of thermodynamics: The expression of the fundamental experiment fact. The first law of thermodynamics: The a statement of conservation of energy for pure thermodynamic system. The second law of thermodynamics: Why we need the second law of thermodynamics?
815.1 why do some things happen, while others do not? 1. Some examples that can not happen One of the sacred truths of physics is the principle of energy conservation. For instance O A rock does not jump spontaneously up to the top of the cliff; ----violate the Cwe theorem 2 Pizza does not warm itself: ----violate the first law of thermodynamics 3 Water cannot become into ice automatically OA drop of ink spread throughout water never regroup into a drop-shaped clump 815.1 why do some things happen, while others do not? It is not the energy of the system that controls the direction of irreversible processes; it is another property that we introduce in this chapter. 2. What is the irreversible processes The isothermal expansion of an ideal gas: 1→H2"H1=Q= nITin2>0 V2→V1W2=Q2=nRTn<0 result W, +W=0 Reversible Q1+Q2=0
2 §15.1 why do some things happen, while others do not? One of the sacred truths of physics is the principle of energy conservation. 1 A rock does not jump spontaneously up to the top of the cliff;----violate the CWE theorem 2 Pizza does not warm itself; ----violate the first law of thermodynamics 3 Water cannot become into ice automatically; 4A drop of ink spread throughout water never regroup into a drop-shaped clump. For instance: 1. Some examples that can not happen It is not the energy of the system that controls the direction of irreversible processes; it is another property that we introduce in this chapter. §15.1 why do some things happen, while others do not? 2. What is the irreversible processes The isothermal expansion of an ideal gas: 1frictionless, quasi-static V1 →V2 ln 0 1 2 1 = 1 = > V V W Q nRT V2 →V1 ln 0 2 1 2 = 2 = < V V W Q nRT result ： 0 W1 +W2 = Q1 + Q2 = 0 Reversible!
815.1 why do some things happen, while others do not? Lead shot Lead Thermal reservoir Control knob (a) Initial state i b) Final state 815.1 why do some things happen, while others do not? @friction, quasi-static V1→V O,=W,+W=nRTIn-+w >0) 2,=Wi+W,=nRTIn -I+w (<0) result 21+o2=2w>0 reversible
3 §15.1 why do some things happen, while others do not? 2friction, quasi-static V1 →V2 Q1 = W1 +W f W f V V = nRT + 1 2 ln (>0) (>0) V2 →V1 Q W +W f = ′ 2 1 W f V V = nRT + 2 1 ln (< 0) (>0) result Q1 + Q2 = 2Wf > 0 Irreversible! ： §15.1 why do some things happen, while others do not?
815.1 why do some things happen, while others do not? @frictionless, not quasi-static 2,=W< Pdv=nRT In Q2|=WP=nRW女 resu ltQ1+Q2=W1+W2<0 The wok done on the system: W2l-W, The heat transfer to the environgiht=o Irreversible! s15.2 heat engines and the second law of thermodynamics 1. Heat engines and refrigerator engines We use the word engine to mean a system such as a gas that performs a closed cycle on P-v diagram. If the cycle is performed clockwise we called it a heat engine: If counterclockwise we called it a refrigerator engine. The function of a heat engine is to transform disordered internal energy into macroscopic work using the heat transfer between reservoirs at different temperatures
4 3frictionless, not quasi-static 1 2 1 1 d ln 2 1 V V Q W P V nRT V ∫V = < = 1 2 2 2 d ln 1 2 V V Q W P V nRT V V = > = ∫ result ： 0 Q1 + Q2 = W1 +W2 < The wok done on the system： W2 −W1 The heat transfer to the environment Q2 −：Q1 Irreversible! §15.1 why do some things happen, while others do not? §15.2 heat engines and the second law of thermodynamics 1. Heat engines and refrigerator engines We use the word engine to mean a system such as a gas that performs a closed cycle on P-V diagram. If the cycle is performed clockwise, we called it a heat engine; If counterclockwise, we called it a refrigerator engine. The function of a heat engine is to transform disordered internal energy into macroscopic work using the heat transfer between reservoirs at different temperatures
s15.2 heat engines and the second law of thermodynamics 2. The efficiency of the heat engines Q W>0 For a cycle: ∠1U=0 total =W=0H -ec s15.2 heat engines and the second law of thermodynamics 的 冷凝器 net 2H-e Q =1 2H 2H 2H
5 2. The efficiency of the heat engines QC TC W For a cycle: Q W QH QC U = = − = total ∆ 0 V P W > 0 §15.2 heat engines and the second law of thermodynamics QH QC W1 W2 H C H H C H Q Q Q Q Q Q W = − − = = 1 net ε §15.2 heat engines and the second law of thermodynamics