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=02 §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!