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