Chapter 2 The First Law of Thermodynamics.ppt

Physical Chemistry Cheng Xuan Exothermic and Endothermic Homework (2.1-2.6) The internal energy Transnational energy, Utr Rotational energy, Urot Vibrational energy, Uvib Electronic energy, Uel Energy due to intermolecular forces, Uintemol Rest-mass energy of the electrons & nuclei, Urest Homework (2.7-2.11) Announcement Chapter 2 Physical Chemistry Joule experiment q = 0 (the system is surrounded by adiabatic walls) A B Adiabatic wall Fig. 2.6 valve thermometer w = 0 (gas expansion into a vacuum) ?U = q + w = 0 + 0 = 0 (a constant-energy process) The experiment measures ?T with ?V at constant internal energy, (2.62) Joule coefficient Physical Chemistry Chapter 2 Joule experiment total differential of z(x,y) (2.62) When y is kept constant (1.30)* total differential of z(r,s,t) When x is kept constant (1.31) Physical Chemistry Chapter 2 Joule experiment Division by dzy gives (2.62) When z stays constant From the definition of the partial derivative (1.32)* (1.33) (1.30)* Physical Chemistry Chapter 2 Joule experiment Division by dyz gives (2.62) Using (1.32) with x and y interchanged and multiplied by (1.34)* Physical Chemistry Chapter 2 Joule experiment Replaced x, y, z with T, U, and V, gives (2.62) When (1.32), (2.53) and (2.62) were used (2.63) Physical Chemistry Chapter 2 Joule-Thomson experiment P1 P1, V1, T1 Porous Plug P2 (a) (b) (c) P1 P2 P2, V2, T2 P1 P1 P2 P2 Adiabatic Wall Fig. 2.7 The Joule-Thomson experiment. P2 < P1 B Physical Chemistry Chapter 2 The slow throttling of a gas through a rigid, porous plug. The system is enclosed in adiabatic walls. The left piston is held at a fixed pressure P1, the right piston is held at a fixed pressure P2 (<P1). The partition B is porous but not greatly so. This allows the gas to be slowly forced from one chamber to the other. Because the throttling process is slow, pressure equilibrium is maintained in each chamber. Essentially all the pressure drop from P1 to P2 occurs in the porous plug. P1 P1, V1, T1 P2 (a)