NEET &#8211; THERMODYNAMICS &#8211; 2024

1. If ΔH is the change in enthalpy and ΔE the change in internal energy accompanying a gaseous reaction, then

(a) ΔHis always greater than ΔE
(b) ΔH< ΔE only if the number of moles of the products is greater than the number of moles of the reactants
(c) ΔH is always less than ΔE
(d) ΔH< ΔE only if the number of moles of products is less than the number of moles of the reactants.

2. Equal volumes of molar hydrochloric acid and sulphuric acid are neutralized by dil. NaOHsolution and x kcal and y kcal of heat are liberated respectively. Which of the following is true?
(a) x = y
(b) x = 1/2
(c) x = 2y
(d) None of these

3. For the reaction N₂ +3H₂ ⇌ 2NH₃ , D H = ?
(a) ΔE+ 2RT
(b) ΔE–2RT
(c) ΔH= RT
(d) ΔE– RT.

4. During isothermal expansion of an ideal gas, its
(a) internal energy increases
(b) enthalpy decreases
(c) enthalpy remains unaffected
(d) enthalpy reduces to zero.

5. Achemical reaction will be spontaneous if it is accompanied by a decrease of
(a) entropy of the system
(b) enthalpy of the system
(c) internal energy of the system
(d) free energy of the system

6. Consider the following reaction occurring in an automobile 2C₈H₁₈(g) +25 O₂(g) ® 16CO₂ + 18 H₂O(g) the sign of DH , Ds and DG would be
(a) +,–,+
(b) –, +, –
(c) –, +, +
(d) +, +, –.

7. Standard Gibb’s free energy change for isomerisation reaction cis -2 – pentene ⇌ trans 2- pentene is -3.67 kJ/ mol at 400K. If more trans -2 penten is added to the reaction vessel, then

(a) more cis-2 pentene is formed
(b) equilibrium remains unaffected
(c) additional trans-2 pentene is formed
(d) equilibrium is shifted in forward direction

8. If enthalpies of formation of C₂H_4(g) , CO_2(g) and H₂O_(i) at 25⁰c and 1 atm pressure are 52, -394 and -286 kJ/mol respectively, the change in enthalpy is equal to

(a) – 141.2 kJ/mol
(b) – 1412 kJ/mol
(c) + 14.2 kJ/mol
(d) + 1412 kJ/mol

9. The correct relationship between free energy and equilibrium constant Kof a reaction is
(a) G⁰ = – RTlnK
(b) G = RTlnK
(c) G⁰ = RTlnK
(d) G = – RTlnK

10. According to the third law of thermodynamics which one of the following quantities for a perfectly crystalline solid is zero
at absolute zero?
(a) Free energy
(b) Entropy
(c) Enthalpy
(d) Internal energy

11.The entropy values (in J/Kmol) of H2(g)=130.6, Cl2(g)=223.0 and HCl=186.7 at 298 K and 1 atm pressure. Then entropy change for the reaction: H₂(g)+Cl₂(g)→2HCl(g) is:

(a) +540.3
(b) +727.0
(c) –166.9
(d) +19.8

12. Hydrogen has an ionisation energy of 1311 kJ mol^-1and for chlorine it is 1256 kJmol^-1. Hydrogen forms H+ (aq) ions but chlorine does
not form Cl⁺(aq) ions because

(a) H+ has lower hydration enthalpy
(b) Cl+ has lower hydration enthalpy
(c) Cl has high electron affinity
(d) Cl has high electronegativity

13.Given that C + O₂ -> CO₂ : DH⁰ = – x kJ 2CO + O₂ -> 2CO₂ : D H⁰ = – y kJ the enthalpy of formation of carbon monoxide will be

(a)
(b)
(c) 2x – y
(d) y -2x

14. Identify the correct statement regarding entropy:
(a) At absolute zero of temperature, entropy of a perfectly crystalline substance is taken to be zero
(b) At absolute zero of temperature, the entropy of a perfectly crystalline substance is +ve
(c) At absolute zero of temperature, the entropy of all crystalline substances is taken to be zero
(d) At 0ºC, the entropy of a perfectly crystalline substance is taken to be zero

15. One mole of an ideal gas at 300 Kis expanded isothermally from an initial volume of 1 litre to 10 litres. The ‘Efor this process is (R=2 cal. Mol^-1K^-1)
(a) 163.7 cal
(b) zero
(c) 1381.1 cal
(d) 9 lit. atm

16. For a cyclic process, which of the following is not true?
(a) ΔH= 0
(b) ΔE= 0
(c) ΔG= 0
(d) Total W= 0

17. Adiabatic expansions of an ideal gas is accompanied by
(a) decrease in ΔE
(b) increase in temperature
(c) decrease in ΔS
(d) no change in any one of the above properties

18. For a reaction in which all reactants and products are liquids, which one of the following equations is most applicable?
(a) ΔH< ΔE
(b) ΔH= ΔS
(c) ΔH= ΔE
(d) ΔH= ΔG

19. The entropy change in the fusion of one mole of a solid melting at 27⁰C(Latent heat of fusion, 2930 Jmol^-1) is:
(a) 9.77 JK^-1mol^-1
(b) 10.73 JK^-1mol^-1
(c) 2930 JK^-1mol^-1
(d) 108.5 JK^-1mol^-1

20.The factor of DG values is important in metallurgy. The DG values for the following reaction at 800⁰C are given as:

S_2(s) + 2O_2(g) -> 2SO_2(g) ; DG = -544kJ

2Zn_(s) + S_2(s) -> 2ZnS_(s) ; DG = – 293 kJ

2Zn_(s) + O_2(s) -> 2ZnS_(s) ; DG = – 480 kJ

Then DG for the reaction :

2Zn_(s) + O_2(s) -> 2ZnS_(s) +2SO_2(g) ; DG = – 293 kJ

Will be
(a) –357 kJ
(b) –731 kJ
(c) –773 kJ
(d) –229 kJ

21. The values of heat of formation of SO₂ and SO₃ are -298.2 kJ and -98.2 kJ. The heat of formation of the reaction SO₂ +(1/2)O₂ -> SO₃ Will be
(a) –200 kJ
(b) –356.2 kJ
(c) + 200 kJ
(d) – 396.2 kJ

22. For a hypothetical reaction A®B, the activation energies for forward and backward reaction are 19 kJ / mole and 9kJ/ mole respectively. The heat of reaction

(a) 28 kJ
(b) 19 kJ
(c) – 10 kJ
(d) 9 kJ

23. Enthalpy of CH₄+ O₂ ®CH₃OH is negative. If enthalpy of combustion of CH₄ and CH₃OH are x and y respectively, then which relation is correct

(a) x > y
(b) x < y
(c) x = y
(d) x ≥ y

24. When 1 mol of a gas is heated at constant volume, temperature is raised from 298 to 308 K. If heat supplied to the gas is 500 J, then which
statement is correct?
(a) q = w = 500 J, ΔU= 0
(b) q = ΔU= 500 J, w = 0
(c) q = –w = 500 J, ΔU= 0
(d) ΔU= 0, q = w = –500 J

25. What is the enthalpy change for, 2H₂O₂ (I) -> 2H₂O(I) +O₂(g) if heat of formation of H₂O₂(I) and H₂O(I) are – 188 and -286 kj/mol respectively ?

(a) –196 kJ/mol
(b) + 948 kJ/mol
(c) + 196 kJ/mol
(d) –948 kJ/mol

26. In a closed insulated container, a liquid is stirred with a paddle to increase the temperature, which of the following is true?
(a) ΔE = W ≠ 0,q = 0
(b) ΔE = W = q ≠ 0
(c) ΔE=0,W=q ≠ 0
(d) W=0, ΔE = q ≠ 0

27. 2 mole of an ideal gas at 27ºCtemperature is expanded reversibly from 2 lit to 20 lit. Find the entropy change (R= 2 cal/mol K)
(a) 92.1
(b) 0
(c) 4
(d) 9.2

28. Heat of combustion DH⁰ for C(s), H₂(g) and CH₄(g) are -94 , -68 and -213 kcal/mol, then DH⁰ for C(s)+2H₂(g)->CH₄(g) is

(a) –17 kcal
(b) – 111 kcal
(c) –170 kcal
(d) –85 kcal

29. Unit of entropy is
(a) JK^-1mol^-1
(b) Jmol^-1
(c) J^-1K^–mol^-1
(d) JKmol^-1

30. The molar heat capacity of water at constant pressure is 75 JK^-1mol^-1. When 1kJ of heat is supplied to 100 g of water, which is free to
expand, the increase in temperature of water is
(a) 6.6 K
(b) 1.2 K
(c) 2.4 K
(d) 4.8 K

31. What is the entropy change (in JK^-1mol^-1`) when one mole of ice is converted into water at 0º C? (The enthalpy change for the conversion of
ice to liquid water is 6.0 kJmol^-1at 0ºC)
(a) 21.98
(b) 20.13
(c) 2.013
(d) 2.198

32. The densities of graphite and diamond at 298 Kare 2.25 and 3.31 g cm^-3, respectively. If the standard free energy difference (ΔGº) is
equal to 1895 Jmol–1, the pressure at which graphite will be transformed into diamond at 298 Kis
(a) 9.92 × 10⁵Pa
(b) 9.92 × 10⁸Pa
(c) 9.92 × 10⁷Pa
(d) 9.92 × 10⁶Pa

33. For which one of the following equation is DH⁰_react equal to DH⁰_f for the product ?

(a) 2CO_(g) + O_2(g) -> 2CO_2(g)
(b) N_2(g) + O_3(g) -> N₂O_3(g)
(c) CH_4(g) +2Cl_(g) -> CH₂Cl_2(l)+ 2HCl_(g)
(d) Xe_(g) + 2F_2(g) -> XeF_4(g)

34. For the reaction C₃H_8(g) +5O_2(g) -> 3CO_2(g) +4H₂O_(l) at constant temperature , DH – DE is

(a) – RT
(b) + RT
(c) – 3 RT
(d) + 3 RT

35. If bond energies of H –H , Br –Br ,and H –Br are 433 , 192 and 364 kJ mol^-1 respectively, the DH^o for the reaction

(a) – 261 kJ
(b) + 103 kJ
(c) + 261kJ
(d) – 103 kJ

36. Standard enthalpy and standard entropy change for the oxidation of ammonia at 298 K -382.64 kJ mol^-1 and -145.6 JK^-1 mol^-1 respectively. Standard Gibb’s energy change for the same reaction 298 K is

(a) -22.1 kJ mol^-1

(b) -339.3 kJ mol^-1
(c) -439.3 kJ mol^–
(d) -523.2 kJ mol^-1

37. Considering entropy as a thermodynamic parameter, the criterion for the spontaneity of any process is
(a) DS_system + DS_urroundings> 0

(b) DS_system – DS_urroundings> 0
(c) DS_system > 0
(d) DS_urroundings> 0

38. The work done during the expansion of a gas from volume of 4dm³ to 6 dm³ against a constant external pressure of 3 atm is (1 Latm = 101.32J)

(a) – 6 J
(b) – 608 J
(c) + 304 J
(d) – 304 J

39. The absolute enthalpy of neutralisation of the reaction

MgO_(s) + 2HCl_(aq) -> MgCl_2(aq) + H₂O_(l) will be

(a) -57.33 kJ mol^-1
(b) Greater than -57.33 kJ mol^-1
(c) Less than -57.33 kJ mol^-1
(d) 57.33 kJ mol^-1

40. A reaction occurs spontaneously if

(a) T D S < D H and both DH and DS are + ve
(b) T D S > D H and DH is + ve and DS are + ve
(c) T D S > D H and both DH and DS are + ve
(d) T D S = D H and both DH and DS are + ve

41. Which of the following pairs of a chemical reaction is certain to result in a spontaneous reaction?
(a) Exothermic and increasing disorder
(b) Exothermic and decreasing disorder
(c) Endothermic and increasing disorder
(d) Endothermic and decreasing disorder

42. The enthalpy of hydrogenation of cyclochexane is -119.5kJ mol^-1 . If resonance energy of benzene is -150.4 kJ mol^-1 , its enthalpy of hydrogenation would be
(a) -208.1 kg mol^-1
(b) -269.9 kg mol^-1
(c) -358.5 kg mol^-1
(d) -508.9 kg mol^-1

43. The enthalpy and entropy change for the reaction Br₂(I)+Cl₂(g) ® 2Brcl(g) are 30kj mol^-1 and 105 kj^-1 mol^-1 respectively. The temperature at which the reaction will be in equilibrium is

(a) 273 K
(b) 450 K
(c) 300 K
(d) 285.7 K

44. Identify the correct statement for the chang of energy for a system (DG_system) at constant temperature and pressure.

(a) if DG _system= 0, the system has attained equilibrium
(b) if DG _system= 0, the system is still moving in a particular equilibrium
(c) if DG _system< 0, the process is not spontaneous
(d) if DG _system> 0, the process is not spontaneous

45. Assume each reaction is carried out in an open container. For which reaction will DH = DE ?

(a) C(s)+2H₂O(g) -> 2H₂(g)+CO₂(g)
(b) PCl₅(g) -> PCl₃(g)+Cl₂(g)
(c) 2CO(g)+O₂(g) -> 2CO₂(g)
(d) H₂(g) +Br₂(g)-> 2HBr(g)

46. Consider the following reactions :

(I) + = H₂O_(l);ΔH=−X₁kJ.mol⁻¹

(II) H₂(g)+ O₂(g)=H₂O(l);ΔH=−X₂ kJ.mol⁻¹

(III) CO₂_(g)+H_2(g)=CO_(g)+H₂O(l);ΔH=+X₃ kJ.mol⁻¹

(IV) C₂H₂_(g)+ O₂_(g)=2CO(g)+H₂O(l);ΔH=+X₄ kJ.mol⁻¹

Enthalpy of formation of H₂O_(l) is:

(a) +X₃ kJ mol^-1
(b) –X₄ kJ mol^-1
(c) +X₁ kJ mol^-1
(d) –X₂ kJ mol^-1

47. Given that bond energies of H- C and Cl – Cl are 430 kJ mol^-1 and 240 kJ mol^-1 respectively and D H_f for HCl is -90 kJ mol^-1 , bond enthalpy of HCl is

(a) 380 kJ mol^-1
(b) 425 kJ mol^-1
(c) 245 kJ mol^-1
(d) 290 kJ mol^-1

48. which of the following are not state functions ?

(I) q + w

(II) q

(III) w

(IV) H – TS

(a) and (IV)
(b) (II) , (III) and (IV)
(c) , (II) and (III)
(d) (II) and (III)

49. For the gas phase reaction, PCl₅(g) ⇌ PCl₃(g) +Cl₂(g)

Which of the following conditions are correct ?

(a) DH = 0 and DS < 0

(b) DH > 0 and DS > 0
(c) DH < 0 and DS < 0
(d) DH > 0 and DS < 0

50. Bond dissociation enthalpy of H₂ , Cl₂ and HCl are 434 , 242 and 431 kJ mol^-1 respectively. Enthalpy of formation of HCl is :

(a) 93 kJ mol^-1
(b) -245 kJ mol^-1
(c) -93 kJ mol^-1
(d) 245 kJ mol^-1

51. The values of D H and D S for the reaction, C_(graphite)+ CO_2(g) ® 2CO_(g) are 170 kJ and 170 kJ^-1 , respectively. This reaction will be spontaneous at

(a) 910K
(b) 1010K
(c) 510K
(d) 710K

52.From the following bond energies:
H−H bond energy : 431.37kJ mol⁻¹
C=C bond energy : 606.10kJ mol⁻¹
C−C bond energy : 336.49kJ mol⁻¹
C−H bond energy : 410.50kJ mol⁻¹
Enthalpy for the given reaction will be