Conductance, Electrochemistry and Chemical Kinetics — DU Physical Science courses pertaining to Chemistry Previous Year Question Papers

2962 (c) Decromposition of Ammonium Nitrite produces Nitrogen gas. Volume of N2 collected at different intervals of time are following. 5 Time/min 10 15 20 24  Prove that the reaction is first order. 6. (a) Discuss the titration curves obtained from conductometric titrations of; 5 (ii) Acetic acid vs NaOH (b) At 250C the molar conductivity of 0.03M AgNO3 solution is 143.2 Scm2mol-1 while the transference number of 3 NO is 0.52. Calculate the molar ionic conductivity and mobility of Ag+ and ions 3 Describe the mechanism of acid catalysed reaction in which acid form of substrate reacts with water. Discuss the cases. 5 Electrochemistry and Chemical Kinetics (c) The questions should be numbered in accordance to the number in the questions paper. 1. Answer any five of the following. 5×3=15 (a) What is the difference between rate constant and rate of reaction. (b) What is the difference between a reversible and an irreversible cell ? Explain with examples of both. (c) Why it is not possible to determine the equivalent conductance of a weak electrolyte at infinite dilution by direct measurement using conductivity meter ? (d) Calculate the free energy change for the reaction of the following cell at 250C. (The standard EMF of the cell is 0.14V) (e) Draw labelled energy profile diagrams for endothermic and exothermic reactions using a catalyst ? (f) Why a first-order reaction never reachs completion ? 2. (a) Define specific conductance, molar conductance and equivalent conductance. Explain why conductivity decreases while equivalent conductivity increases on dilution. 5 (b) If the molar conductance at infinite dilution of NaCl, HCl and CH3COONa are 126, 420, and 91 Scm2mol-1, respectively, calculate the molar conductance of acetic acid at infinite dilution. 5 (c) The kinetics of enzyme catalyzed reaction is studied by Michaelis-Menton mechanism. Using the suitable approximation, relate enzyme and substrate concentration to the rate of the reaction. Also discuss how the rate of reaction varies when Michaelis-Menton constant is greater than enzyme concentration. 5 3. (a) How does the rate of a reaction depend on temperature ? The activation energy of a reaction is 22.5 kcalmol-1. Its specific rate constant is 1.8 × 10-5 sec-1. Calculate the Pre-exponential factor (A) 4. (b) How do we use glass electrode for the determination of pH of a given solution ? What are advantages and disadvantages of glass electrode ? 5 (c) For the electrochemical cell. The EMF at 00C and 250C are 0.6915 V and 0.6753 The cell reaction is : Cd(s) + 2AgCl(s) + H2O  CdCl2.5/2 H2O (sat.) + 2Ag(s) Calculate the  G0 (a) What is the significance of the order of a reaction ? Show that the units of specific rate constant are different for reactions of zero, first and second order. (b) (c) The half-life of a first order decomposition reaction at 650K is 363 min and its activation energy is 220 kJ/mol. Calculate the rate constant for this reaction at 720K. 5