14 Thermodynamics and Thermochemistry . The reaction, MgO(s) + C(s) Mg(s) + CO(g ) 18 The entropy change associated with the conversion of 1 kg of ice at 273 K to water vapours at 383 K is for which A, H = + 491.1 kJ mol and (Specific heat of water liquid and water vapour are 4.2 kJ Kkg and 20 kJK kg; heat of liquid fusion and A,S = 198.0 JK-'mol-, is not feasible at 298 K. Temperature above which reaction will be feasible is (a) 2040.5 K (c) 2380.5 K (b) 1890.0 K (d) 2480.3 K vapourisation of water are 334 kJ kg and 2491 kJkg (log 273 = 2436, respectively). log 383 = 2583) (a) 9.26 kJ kg K-1 log 373 = 2.572, (2019 Main, 9 Jan II) The standard reaction Gibbs energy for a chemical reaction at an absolute temperature T is given by, A,G = A- BT Where A and B are non-zero constants. (b) 849 kJ kg'K- (d) 264 kJ kg'K-1 (c) 7.90 kJ kg-'K-1 Which of the following is true about this reaction? 19 Consider the reversible isothermal expansion of an ideal gas in a closed system at two different temperatures T and T2 (T 0 (b) Exothermic if, B < 0 (c) Exothermic if, A >0 and B 0 |W| T2 |W| For the chemical reaction, X Y, the standard reaction Gibbs energy depends on temperature T (in K) as (a) 4,G (in kJ mol) = 120 -T 8 (b) The major component of the reaction mixture at T is In V In V (2019 Main, 11 Jan I) (b) Xif T=350 K (d) Y if T = 300 K (a) Y if T=280 K T2 |W| T2 (c) X if T=315 K . Two blocks of the same metal having same mass and at temperature T and T, respectively, are brought in on with each other and allowed to attain thermal equiljbriamat constant pressure. The change in entropy, process is (c) (d) In V In V (T; + T; }'2 TT, 20. The combustion of benzene (1) gives CO,(g) and H2O(1). (a) Cp ,In (b) ?C, In Given that heat of combustion of benzene at constant volume T + T, (d) ?C, In 27,T, is -3263.9 kJ mol at 25 C; heat of combustion (in kJ mol) of benzene at (R = 8.314 JK'mol) (T + () , In constant pressure will be 4TT, (2018 Main) (b) -45246 (d) -3267.6 . The process with negative entropy change is (a) 4152.6 (2019 Main, 10 Jan II) (c) 3260 (a) synthesis of ammonia from N, and H, (b) dissociation of CaSO,(s) to Ca0(s) and SO, (g) (c) dissolution of iodine in water (d) sublimation of dry ice 21. AU is equal to (a) isochoric work (c) adiabatic work (2017 Main) (b) isobaric work (d) isothermal work 22. The standard state Gibbs free energies of formation of C(graphite) and C(diamond) at T = 298 K are . An ideal gas undergoes isothermal compression from 5 m3 to 1 m' against a constant external pressure of 4 Nm2. Heat released in this process is used to increase the temperature of 1 mole of Al. If molar heat capacity of Al is 24 J mol 'K, A,G[Cgraphite)] = 0kJ mol -1 A,G[adiamond)] = 2.9 kJ mol" the temperature of Al increases by (2019 Main, 10 Jan II) The standard state means that the pressure should be 1 bar, and substance should be pure at a given temperature. The conversion of graphite [C(graphite)] to [C(diamond)] reduces its volume by 2x 10 6 m mol. If () 2 (b) IK (c) 2 K (d) K diamond 7 A process has AH = 200 J mol and AS = 40 JK- mol-!. Out of the values given below, choose the minimum temperature above which the process will be spontaneous (2019 Main, 10 Jan I) C(graphite) is converted to C(diamond) isothermally at T = 298K, the pressure at which C(graphite) is in equilibrium with C(diamond), is (2017 Adv.) : (a) 20 K (b) 4 K (c) 5 K (d) 12 K 6 tmeljeelibrary