Question

BEng 3M - 2019/20:SEMI THERMODYNAMICS II (ENG3002) Tutorial: Topic #2 - Gibbs Eqns and Maxwell Relations QUESTION 1. Pressure (bar) Temperature 60 80 100 5 6 7 8 Cylinder Cylinder Cylinder Cylinder Volume Volume Volume Volume (m (m) m ( m ) 0.2695 0.22150 1872 0.1614 0.2923 0.2412 0.20470 1772 031410 259002210 1919 0 33540277002367 0 2059 03562 0.2955 02521 0 2105 037680.31290 2671 0 2328 0.3973 0 33 0.282 02452 0.4176 03470 2967 0 2589 0.4377036390.31130 2717 140 160 180 Table 1: Superheated P-T information for gas chemical The thermodynamic properties of a gas chemical is being prepared by analyzing data from a set of simple experiments. As shown in the diagram, an oil bath is used to establish the temperature, and a force applied to the top of the piston is used to establish the pressure to the 1 kg of gas contained in a frictionless piston-cylinder device. For a fixed pressure, the volume of the gas at each incremental increase in temperature is recorded. Four such experiments were performed at four different pressures. 5, 6, 7 and 8 bars. The measured values are shown in the table above. (a) *Estimate of the gas at 100 °C and 6 bar. [4 marks] (b) If the gas at 100 °C and 6 bar is very slowly and incrementally pressurized to 6.05 bar, while quasi c ibum maintaining equilibrium with the oil bath, estimate the change in entropy of the gas [4 marks] (c) "For the same process described in Part (b), estimate heat added or removed from the gas. [2 marks] (d) For the same process described in Part (b), estimate the work done to compress the gas. [2 marks] (e) For the same process described in Part (b), estimate change in the internal energy of the gas. [3 marks) (f) For the same process described in Part (b), estimate change in the enthalpy of the gas. [3 marks] (g) *In the space provided on the worksheet, plot versus P at 20, 100, and 180 °C. [4 marks] (h) Rased on the criteria for which the ideal gas assumption is valid, analyze the plot to determine the gas constant for the gas being tested. [3 marks] (1) Determine the molecular weight of the gas. [3 marks] 0) For this same gas, estimate the specific volume at 400 °C and 0.1 bar. [5 marks]

Answer 1

a lay) - 0.2955–0.2778 – 8.858 104 m?k 100 - 80 (We took data less than 100C at 6 bar (constant) because we are compressing the gas (b) from Maxwell eqra (a) = (28) = 8.85x10 ), = -8185x104 AS = -8.85x109x 0.05x109--4425 Ilk (C) Heat removed - TAS = (100 +273) (4.425) = 1650.5 (d) T = 100°c - (Isothermal) Work done for isothermal = Piv, ln 192 = 64105 x 0.2955 do 6.05 = 1471.385 (e) a = BU+W - DU= Q-W= 1650.5-1471.38 100 = 174.125 (f) h=u+pV Here poocess is iso thermal. So, PV = constant. APV)=0 sh = AU+ ALPV) = Du = 179.12 J.