Chemical Energetics and Equilibria (DSC-7, Chemistry-03) — DU B. Sc. Life Science (Chemistry) Previous Year Question Papers

3. The questions should be numbered in accordance to the number in the question paper. Values of constant : R = 8.314 JK' mol' or 1:987 cal K' mot! or 0.082 atm dm? K! mot' (a) What are extensive variables? Identify the extensive variables among the following. specific heat capacity, molar volume, enthalpy, chemical potential, free energy. (b) The Joule coefficient of an ideal gas is zero. (c) The enthalpy of neutralization of strong : id with strong base is constant. Give reason. (d) At constant temperature and pressure, Gibbs free energy attains a minimum value at equilibrium (dGT.p = 0). Justify this statement. (e) What are buffer solutions? Give one example of acidic buffer and basic buffer. (f) Draw the pH metric titration curve of strong acid vs strong base. What is the pH at equivalence point? (3×5) 2. (a) Applying the first law of thermodynamics, prove that heat is an inexact differential. (b) Describe the Joule's experiment. Write the mathematical expression that the energy of a gas is a function of temperature only. (c) 7.0 g of N2 at 25°C is subjected to reversible isothermal expansion from initial pressure of 0.505 MPa to final pressure of 0.202 MPa. Calculate q, w, AU and AH. (5x3) 3. (a) State Hess's law of constant heat summation. Describe the Born Haber Cycle for the determination of lattice energy of NaCl. (b) Define integral enthalpy of solution. Enthalpy of neutralization of HCl by NaOH is -57.32 kJ mol-l and by NH OH is -51.34 kJ mol-! • Calculate enthalpy of dissociation of NH OH. (c) On the basis of following data, evaluate the standard enthalpy of formation of tungsten carbide (iii) C(graphite) + O,(g) → CO, (g) 4. (a) Define heat capacity. Prove that for an ideal gas Cp,m - Cum = R (for 1 mole of an ideal gas) (b) Derive the expression for change in entropy function when the amount n mole of an ideal gas undergoes change from temperature T, and volume V, to temperature T, to volume V (c) Prove that the change in Gibbs free energy at constant temperature and pressure is equal to the net amount of non-mechanical work done. (a) Derive the expression of equilibrium constant of a weak electrolyte AB in terms of degree of dissociation a and concentration c. Also prove that a → 1 as c → 0. (b) The pH of pure water at 40°C is found to be 6.765. What is the value of pK, w? What will be the nature of the solution at 40°C having [H*] = 0.54 x 10-7M. What will be the pOH of the solution. (c) A buffer is made by adding 25.0 cm of 0.1M Sodium acetate to 50.0 cm of 0.1M acetic acid (pk, = 4.75). Write the Henderson-Hasselbalch equation and determine pH of the solution. What would be the pH if this buffer is added to: (i) 25.0 cm? of distilled water 6. (a) Define solubility product of sparingly soluble salt. What is the solubility of Agz(CrO.) in water if the value of solubility product is (b) At 1105 K, the value of K° for a reaction (i) the standard free energy change for this reaction at 1105K