Chemical Thermodynamics and Its Applications — DU B.Sc (hons) Chemistry Previous Year Question Papers

200RO?X* Thermodynamics and its Applications 1. Answer the following questions (Any five): (a) Explain why Hr (Joule Thomsoncoefficient) negative value corresponds to warming and positive value corresponds to cooling. (b) The entropy of crystalline ice is not zero at (c) Why is the work done in isothermal free expansion is zero. (d) In a mixture of two liquids usually why is V, *n, Vi +n, V2. Here V, is the total volume of the mixture, n,, n, are the number of moles of the two liquids and Vi, V2 are the molar volumes of liquid 1 and 2 respectively. (e) The Helmholtz free energy function is sometimes referred to as the work function. (f) Enthalpies of neutralization of different weak acids with the same strong base are different. (b) (i) Calculate the amount of heat supplied to Carnot's cycle working between 368K and 268 K if the maximum work obtained is 895 Joules. 3 (ii) Calculate the free energy change accompanying the compression of 1 mol of COz from 5 atm to 50 atm. Assume that CO, behaves like an ideal gas. 2 (c) The partial molar volume of ethanol in a 60 mole % ethanol-water solution is 57.5cm3 mol. The density of solution is 0.849gcm3, Calculate the partial molar volume of water in the solution. 5 3. (a) Derive the relationship between heat of reaction at constant pressure and at constant volume. For the reaction 2A, (s) + 5B, (g) → 2A,B, (g), what will be the enthalpy of reaction at 298K if its (b) Derive the following relations: 5 (ii) For adiabatic irreversible expansion (c) Describe Joule's experiment with a diagram for ideal gas and the results obtained from it mathematically. 5 4. (a) Prove that isothermal reversible work of expansion is greater than isothermal irreversible expansion W rev > Wi irr (b) Derive the following relation for an ideal gas: (c) (i) Derive the relations for the temperature dependence of enthalpy of reaction, when C, is independent of temperature and dependent on temperature. 3 (ii) If the standard heat of formation of HCI gas at 25°C is - 22.6 kCal mol', what would be its value at 60°CPC, for H,(g) = 6:82 Cal mol' deg' 5. (a) Prove that heat (g) is not a state function and dq is not an exact differential. (b) Show that = O for an ideal gas and is equal to V for solids and liquids. 5 (c) (i) Define and explain the second law of thermodynamics. 3 (ii) What is Trouton's rule. 2 6. (a) Five moles of an ideal gas at 27°C expand from an initial pressure of 10atm to a final pressure of 5 atm against a constant external pressure 1 atm. •Calculate (b) (i) Show that the work done by an ideal gas in a reversible adiabatic expansion from P.V, to P,V, is given by w- PV - RiV, y-1 (ii) Define the standard state of substance. (c) (i) How are absolute values assigned to entropies of different substances? 2 (ii) Calculate the entropy change corresponding to transferring 2 mol of liquid ammonia at a pressure of 101.325kPa from - 40°C to the gaseous state at 200°C. Given C, (NH,) (g) = 33.64 JK 'mol' and