- Assignment 2 Question 1 23 Marks 1 1 The Definition Of Gibbs Free Energy Is Represented By G H Ts Where H T And 1 (47.92 KiB) Viewed 29 times
Assignment 2 Question 1 [23 marks! 1.1 The definition of Gibbs free energy is represented by: G - H - TS Where H. T. and S are enthalpy, temperature and entropy respectively. Similarly, another thermodynamic variable, Helmholtz free energy, A, is defined as A-U-TS Where U is the internal energy. Assume the system as an ideal gas system. State clearly what assumptions that you are making and what process that are using. (a) Show that the following relationship is true: dA=-pdV-SAT where V, is the volume of the system and p is the pressure. (5) (b) How can you use change in Helmholtz free energy to determine the spontaneity of the process? (c) The physical meaning of change in Gibbs free energy (G) is the maximum work that the system can do in a constant temperature and pressure process. What is the physical meaning of the change in Helmholtz free energy? (d) Calculate the change in Helmholtz free energy, MA in kJ). when one mole of an ideal gas at 298 and 25 atm is expanded isothermally and reversibly to a pressure of 13.5 atm. (3) 1.2 The standard molar entropy of NH; is 192.45J.K'.mol-', and its heat capacity is given by the equation Cp. (J.K'.moll) - a + b + c/T' with the coefficients given in the table below. b/(10) cl(10K) NH; 25.1 -155 a 29.75 Calculate the entropy change when one mole of NH; is heated at a constant pressure from 298 K to 373 K. (8) 5