Section A
Q1.
(a) Write the van der Waals equation and explain the physical significance of van der Waals constants a and b.
(b) Why do hydrogen and helium show exceptional behaviour while discussing with van der Waals equation?
(c) C_{60} molecules are cubic close-packed to form the solid C_{60} unit cell. Draw the unit cell and find the number of carbon atoms present in the unit cell.
(d) A simple cubic crystal diffracts an X-ray beam (λ = 3 \text Å) at an angle of 17.5°. Identify the set of planes that cause this diffraction. Given that a = 5 \text Å.
(e) Explain the physical significance of chemical potential. How is it related to Gibbs free energy?
(f) Write the equation for Debye-Hückel limiting law for mean activity coefficient of an ion and explain the meaning of each term involved. Why is this law called limiting law?
(g) The rate constant for the reaction 2HI(g) → H2(g) + I2(g) is 1.33 × 10-6 dm3 mol-1 s-1 at 575 K and 2.50 × 10-3 dm3 mol-1 s-1 at 716 K. Calculate the value of activation energy of the reaction.
(h) Among the electrolytes Na2SO4, CaCl2, Al2(SO4)_3 and NH4Cl, which one is the most effective coagulating agent for Sb2S3 sol?
(i) Calculate the standard reduction potential at 298 K for the reaction Na^ + (aq) + e^- → Na (s) with respect to standard hydrogen electrode. For the overall reaction \Deltar H\circ = 240 \cdot 1 \text kJ mol-1; \Deltar S\circ = -73 \cdot 1 \text J K-1 \text mol-1
(j) Calculate the pH of the solution containing a mixture of quinone and hydroquinone (1:1) in the cell, SCE | solution |H2Q, Q, Pt. The measured EMF of the cell is 0.221 V at 298 K; ESCE\circ = 0.242 V and EH2Q, Q\circ = 0.699 V.
