Thermodynamics

680 | Thermodynamics(a) proportional to the enthalpy of vaporization h fg at thattemperature.(b) proportional to the temperature T.(c) proportional to the square of the temperature T.(d) proportional to the volume change v fg at that temperature.(e) inversely proportional to the entropy change s fg at thattemperature.12–93 Based on the generalized charts, the error involvedin the enthalpy of CO 2 at 350 K and 8 MPa if it is assumed tobe an ideal gas is(a) 0 (b) 20% (c) 35% (d) 26% (e) 65%12–94 Based on data from the refrigerant-134a tables, theJoule-Thompson coefficient of refrigerant-134a at 0.8 MPaand 100°C is approximately(a) 0 (b) 5°C/MPa (c) 11°C/MPa(d) 8°C/MPa (e) 26°C/MPa12–95 For a gas whose equation of state is P(v b) RT,the specified heat difference c p c v is equal to(a) R (b) R b (c) R b (d) 0 (e) R(1 + v/b)Design and Essay Problems12–96 Consider the function z z(x, y). Write an essay onthe physical interpretation of the ordinary derivative dz/dxand the partial derivative (z/x) y . Explain how these twoderivatives are related to each other and when they becomeequivalent.12–97 There have been several attempts to represent the thermodynamicrelations geometrically, the best known of thesevusahFIGURE P12–97being Koenig’s thermodynamic square shown in the figure.There is a systematic way of obtaining the four Maxwell relationsas well as the four relations for du, dh, dg, and da fromthis figure. By comparing these relations to Koenig’s diagram,come up with the rules to obtain these eight thermodynamicrelations from this diagram.12–98 Several attempts have been made to express the partialderivatives of the most common thermodynamic propertiesin a compact and systematic manner in terms ofmeasurable properties. The work of P. W. Bridgman is perhapsthe most fruitful of all, and it resulted in the well-knownBridgman’s table. The 28 entries in that table are sufficient toexpress the partial derivatives of the eight common propertiesP, T, v, s, u, h, f, and g in terms of the six properties P, v, T,c p , b, and a, which can be measured directly or indirectlywith relative ease. Obtain a copy of Bridgman’s table andexplain, with examples, how it is used.TgP