2020 Mains Question Paper I

https://www.upsc.gov.in/sites/default/files/CHEMISTRY_I_1.pdf

Q1a. The dissociation energy decreases on going from N2 to N2+ whereas it increases on going from O2 to O2+.  Explain.

Q1b.  An orthorhombic unit cell has the following parameters: a=0.5A, b=1.0A, c=1.5A.  What will be the smallest spacing between two successive 123-planes?

Q1c.  Express heat capacity at constant volume (Cv) of a substance in terms of its internal  energy (U) and show that {dCv/dV}T,n = 0; for ideal gas

Q1d. Phenol and water are partially miscible liquids.  By mixing these two liquids, we get two phases in equilibrium.  Find the number of degrees of freedom of the system and mention themwith the help of its phase diagram.

Q1e. The equilibrium constant for the reaction
        Fe3+ (aq) + Ag (s) = Fe2+(aq) + Ag+(aq); is 0.531 at 298 K.  Calculate E*Ag+(aq)/Ag(s) when
        E*Fe3+(aq)/Fe2+(aq) = 0.770 V at 298K.

Q2a.  1.0 mol of monoatomic ideal gas expands to double of its initial volume against a constant pressure under isothermal condition of 300K.  Calculate the heat involved.  

Q2b.  A person claims that a heat engine exchanges heat with reservoirs at 300 and 500K, produces 450J of work per 1000J of heat extracted from the hot reservoir.  Is his/her claim feasible? Give reason(s) to support your answer.

Q2c. Consider the following opposing reaction: A = B (both are elementary)
        Depict the plots of concentration of A and B as a function of time and explain.  Given k1/k2=2

Q2d. Show that a surface catalysed decomposition reaction follows zero order kinetics with respect to reactant when its pressure is high enough. 

Q3a.  The wave function of hydrogen atom is is given by R1s= 1/root pie e power -r (in atomic units).  What will be the most probable distance of an electron from the nucleus in its ground state (in unit of a0, the Bohr radius and in A* unit)?

Q3b. 

Paper II: - 

https://www.upsc.gov.in/sites/default/files/CHEMISTRY_II_1.pdf