1. Select the most apropriate option.

    i. The correct thermodynamic
    conditions for the spontaneous
    reaction at all temperatures are
    a. ΔH < 0 and ΔS > 0
    b. ΔH > 0 and ΔS < 0
    c. ΔH < 0 and ΔS < 0
    d. ΔH < 0 and ΔS = 0

    Solution

    ii. A gas is allowed to expand in a well insulated container against a constant external pressure of 2.5 bar from an initial volume of 2.5 L to a final volume of 4.5 L. The change in internal energy, ΔU of the gas will be

    a. -500 J

    b. + 500 J
    c. -1013 J

    d. + 1013 J

    Solution

    iii. In which of the following, entropy of the system decreases?

    a. Crystallization of liquid into solid
    b. Temperature of crystalline solid is increased from 0 K to 115 K
    c. H2(g)→ 2H(g)

    d. 2 NaHCO3(s) →Na2CO3(s) + CO2(g) + H2O(g)

    Solution

    iv. The enthalpy of formation for all elements in their standard states is
    a. unity
    b. zero
    c. less than zero
    d. different elements

    Solution

    v. Which of the following reactions is exothermic?


    a. H2(g) →2H(g)
    b. C(s)→ C(g)
    c. 2 Cl(g) →Cl2(g)
    d. H2O(s)→ H2O(l).

    Solution

    vi. 6.24 g of ethanol are vaporized by supplying 5.89 kJ of heat. Enthalpy of vaporization of ethanol will be
    a. 43.4 kJ mol-1
    b. 60.2 kJ mol-1
    c. 38.9 kJ mol-1
    d. 20.4 kJ mol-1

    Solution

    vii. If the standard enthalpy of formation of methanol is -238.9 kJ mol-1 then entropy change of the surroundings
    will be
    a. -801.7 J K-1

    b. 801.7 J K-1
    c. 0.8017 J K-1

    d. -0.8017 J K-1

    Solution

    viii. Which of the following are not state functions?
    1. Q + W            2. Q                3. W                4. H-TS

    a. 1,2 and 3

    b. 2 and 3
    c. 1 and 4

    d. 2,3 and 4

    Solution

    ix. For vaporization of water at 1 bar, ΔH = 40.63 kJ mol-1 and ΔS = 108.8 J K-1 mol-1. At what temperature, ΔG = 0 ?
    a. 273.4 K

    b. 393.4 K
    c. 373.4 K

    d. 293.4 K

    Solution

    x. Bond enthalpies of H-H, Cl-Cl and H-Cl bonds are 434 kJ mol-1, 242 kJ mol-1 and 431 kJ mol-1, respectively. Enthalpy of formation of HCl is
    a. 245 kJ mol-1

    b. -93 kJmol-1
    c. -245 kJ mol-1

    d. 93 kJ mol-1

    Solution

    2. Answer the following in one or two sentences.

    i. Comment on the statement: no workis involved in an expansion of gas in vacuum

    Solution

    ii. State the first law of thermodynamics

    Solution

    iii. What is enthalpy of fusion?

    Solution

    iv. What is standard state of a substance?.

    Solution
    v. State whether ΔS is positive, negative or zero for the reaction 2H(g) →H2(g). Explain.
    Solution

    vi. State second law of thermodynamics in terms of entropy.

    Solution

    vii. If the enthalpy change of a reaction is ΔH how will you calculate entropy of surroundings?

    Solution

    viii. Comment on spontaneity of reactions for which ΔH is positive and ΔS is negative.

    Solution

    3. Answer in brief.

    i. Obtain the relationship between ΔG0 of a reaction and the equilibrium constant.

    Solution

    ii. What is entropy? Give its units.

    Solution

    iii. How will you calculate reaction enthalpy from data on bond enthalpies?

    Solution

    iv. What is the standard enthalpy of combustion ? Give an example.

    Solution

    v. What is the enthalpy of atomization?
    Give an example.

    Solution

    vi. Obtain the expression for work done in chemical reaction.

    Solution

    vii. Derive the expression for PV work

    Solution

    viii. What are intensive properties?
    Explain why density is intensive property.

    Solution
    ix. How much heat is evolved when 12 g of CO reacts with NO2 ? The reaction is : 4 CO(g) + 2 NO2(g) → 4 CO2(g) + N2(g), ΔrH0 = -1200 kJ
    Solution

    4. Answer the following questions.

    i. Derive the expression for the maximum work.

    Solution

    ii. Obtain the relatioship between ΔH and ΔU for gas phase reactions.

    Solution

    iii. State Hess’s law of constant heat summation. Illustrate with an example. State its applications.

    Solution

    iv. Although ΔS for the formation of two moles of water from H2 and O2 is -327JK-1, it is spontaneous. Explain. (Given ΔH for the reaction is -572 kJ).

    Solution

    v. Obtain the relation between ΔG and ΔStotal Comment on spontaneity of the reaction.

    Solution

    vi. One mole of an ideal gas is compressed from 500 cm3 against a constant external pressure of 1.2 × 105 Pa. The work involved in the process is 36.0 J. Calculate the final volume. (200 cm3)

    Solution

    vii. Calculate the maximum work when 24 g of O2 are expanded isothermally and reversibly from the pressure of 1.6 bar to 1 bar at 298 K.

    Solution
    viii. Calculate the work done in the decomposition of 132 g of NH4NO3 at  100 0C. NH4NO3(s)→ N2O(g) + 2 H2O(g) State whether work is done on the system or by the system.
    Solution
    ix. Calculate standard enthalpy of reaction, Fe2O3(s) + 3CO(g)→ 2 Fe(s) + 3CO2(g), from the following data. ΔfH0(Fe2O3) = -824 kJ/mol, ΔfH0(CO) = -110 kJ/mol, ΔfH0(CO2) = -393 kJ/mol
    Solution

    x. For a certain reaction ΔH0 =219 kJ and ΔS0 = -21 J/K. Determine whether the reaction is spontaneous or nonspontaneous.

    Solution
    xi. Determine whether the following reaction is spontaneous under standard state conditions. 2 H2O(l) + O2(g)→ 2H2O2(l) if ΔH0 = 196 kJ, ΔS0 = -126 J/K Does it have a cross-over temperature? (Nonspontaneous, No)
    Solution
    xii. Calculate ΔU at 298 K for the reaction, C2H4(g) + HCl(g)→ C2H5Cl(g), ΔH = -72.3 kJ How much PV work is done? Ans. : (-69.8 kJ, 2.48 kJ)
    Solution

    xiii. Calculate the work done during synthesis of NH3 in which volume changes from 8.0 dm3 to 4.0 dm3 at a constant external pressure of 43 bar. In what direction the
    work energy flows?
    Ans. : (17.2 kJ, work energy flows into system)

    Solution
    xiv. Calculate the amount of work done in the (a) oxidation of 1 mole HCl(g) at 200 0C according to reaction. 4HCl(g) + O2(g) →2 Cl2(g) + 2 H2O(g) (b) decomposition of one mole of NO at 300 0C for the reaction 2 NO(g)→ N2(g) + O2 Ans. : (a = + 983 kJ ; b = 0 kJ)
    Solution
    xv. When 6.0 g of O2 reacts with CIF as per 2Cl F(g) + O2(g) →Cl2O(g) + OF2(g) The enthalpy change is 38.55 kJ. What is standard enthalpy of the reaction ? (ΔrH0 = 205.6 kJ)
    Solution

    xvi. Calculate the standard enthalpy of formation of CH3OH(l) from the following data
    i.CH3OH(l)+ 32O2(g)  →CO2(g)+ 2H2O(l), ΔH0 = -726 kJ mol-1

     

    ii. C (Graphite) + O2(g) →CO2(g), ΔcH0 = -393 kJ mol-1

     

    iii. H2(g) + 12 O2(g)→ H2O(l), ΔfH0 = -286 kJ mol-1

    Ans. : (- 239 kJ mol-1)

    Solution
    xvii. Calculate ΔH0 for the following reaction at 298 K H2B4O7(s) + H2O(l) 4HBO2 (aq) i. 2H3BO3(aq)→ B2O3(s) + 3H2O(l), ΔH0 = 14.4 kJ mol-1 ii. H3BO3(aq)→ HBO2(aq) + H2O,(l) ΔH0 = -0.02 kJ mol-1 iii. H2B4O7(s)→ 2P2O3(s) + H2O(l), ΔH0 =17.3 kJ mol-1 Ans. : (- 11.58 kJ)
    Solution

    xviii. Calculate the total heat required (a) to melt 180 g of ice at 0 0C, (b) heat it to 100 0C and then (c) vapourise it at that
    temperature. Given ΔfusH0(ice) = 6.01 kJ mol-1 at 0 0C, ΔvapH0(H2O) = 40.7 kJ mol-1 at 100 0C specific heat of water is 4.18 J g-1 K-1 Ans. : (542.3 kJ)

    Solution
    xix. The enthalpy change for the reaction, C2H4(g) + H2(g) →C2H6(g) is -620 J when 100 ml of ethylene and 100 mL of H2 react at 1 bar pressure. Calculate the pressure volume type of work and ΔU for the reaction. Ans.: (W = +10.13 J; ΔU = -609.9 J)
    Solution

    xx. Calculate the work done and comment on whether work is done on or by the system for the decomposition of 2 moles of NH4NO3 at 100 0C NH4NO3(s) N2O(g) + 2H2O(g)
    Ans. (-18.61 kJ, work is done by the system)

    Solution