8 17-5 Some Special Cases of The First Law of Thermodynamics(P409-417) 1. Isothermal ( Constant-Temperature) Process:P409 The process carried out at constant temperature 特征=常量 过程方程p=常量 M i △ R△TdU=0 RT Or=w=n dv= nRT hn nRT In p1
§ 17-5 Some Special Cases of The First Law of Thermodynamics (P409-417) 1. Isothermal (Constant-Temperature) Process: P409 The process carried out at constant temperature. dU = 0 特征 T = 常量 过程方程 pV = 常量 R T M i U = 2 = = = V V RT Q W n V V T d 2 1 1 2 V V nRT ln 2 1 p p = nRT ln
2. Isochoric(Constant-Volume) Process(p410) The volume of the system is held constant, no work is done for the system 特征:d=0 VEC dW=pdv=0,orW=0→9=△U >0, system absorbs heat from its environment; △U <0, then the system releases heat. P State Equation P = const。 or T T172 V=const
U > 0, system absorbs heat from its environment; < 0, then the system releases heat. dW=pdV=0, or W=0 → Q = U 2. Isochoric (Constant-Volume) Process (p410): The volume of the system is held constant, no work is done for the system. = const. T p V p V=const. II o I State Equation: 2 2 1 1 T p T p or, = 特征： dV=0 V=C
3. Isobaric(Constant-Pressure)Process(P410) The presure of the system is held constant. 特征:dp=0dW=pdV P=C Q=△U+W The heat absorbed by gas is used for increasing its internal energy and doing work气体吸收的热 量一部分用于增加内能,另一部分用于对外作功。 State equation const 0
The heat absorbed by gas is used for increasing its internal energy and doing work 气体吸收的热 量一部分用于增加内能，另一部分用于对外作功。 Q = U +W dW=pdV 3. Isobaric (Constant-Pressure) Process (P410): The presure of the system is held constant. = const. T V p =C 特征：dp=0 V p II o I Vi Vf State Equation:
4. Adiabatic Process(绝热过程):p409 特征dQ=0 热一律dW+dU=0dW=-dU The change of the internal energy is by the amount of work <0, if the work is done by the system △U >0, if the work is done on the system
4. Adiabatic Process (绝热过程): p409 特征 dQ = O 热一律 dW +dU = 0 dW = −dU —— The change of the internal energy is by the amount of work. U < 0, if the work is done by the system. > 0, if the work is done on the system
5. Adiabatic free expansion:绝热自由膨胀(p412) 特征:由于过程是绝热的,dQ=0 由热力学第一定律dW+dU/=0 由于气体是向真空中冲入,所以它对外界不做功,即 dW=0 所以,7=0即U2-U1 即气体经过自由膨胀,内能保持不变。 对于理想气体,内能只包含分子的热运动动能,它 只是温度的函数,所以经过自由膨胀,理想气体再 达到平衡态时,它的温度复原
5. Adiabatic Free Expansion:绝热自由膨胀(p412) 特征：由于过程是绝热的， dQ = O 由热力学第一定律 dW +dU = 0 由于气体是向真空中冲入，所以它对外界不做功，即 dW=0 即气体经过自由膨胀，内能保持不变。 对于理想气体，内能只包含分子的热运动动能，它 只是温度的函数，所以经过自由膨胀，理想气体再 达到平衡态时，它的温度复原。 所以， dU = 0 即 U2 −U1 即：T2=T1