# Thermodynamics Questions And Answers Pdf

The zeroth law of thermodynamics states that if two thermodynamic systems are each in thermal equilibrium with a third, then they are in thermal equilibrium with each other. This law is the basis for the temperature measurement. The first law of thermodynamics states that energy cannot be created or destroyed in an isolated system; energy can only be transferred or changed from one form to another. The first law of thermodynamics is a restatement of the law of conservation of energy.

i.e., According to the first law of Thermodynamics:. Now the First Law of Thermodynamics helped us in understanding the principle of conservation of energy, whereas according to the Second Law of thermodynamics for natural system heat always flows in one direction (higher temperature to lower temperature body) unless it aided by an external factor.

And to measure the direction of force we use term entropy which can be expressed as.

$${\rm{\Delta }}S = \;\smallint \frac{{dQ}}{T}$$.

ΔQ = heat exchange. ΔW = work done due to expansion.

ΔU = internal energy of the system.

ΔS = change in entropy. T = temperature.

As explained above according to the first law of thermodynamics energy cannot be created or destroyed in an isolated system, energy can only be transferred or changed from one form to another.

This is the ideal statement which is used in thermodynamics for explaining the concept of energy conservation among systems and surrounding.

Hence option 2 is correct among all.

Tricks to remember:.

This is the conclusive point for all three laws of thermodynamics.

Zeroth law – Concept of temperature.

First law – Concept of internal energy/ energy conservation.

Second law – Concept of entropy/ heat flow.

(B) The system in equilibrium state or moving from one equilibrium state to another equilibrium state.

C. Both of these

D. None of these

Answer: Both of these

4. Thermodynamics is not concerned about______.

(A) energy changes involved in a chemical reaction.

(B) the extent to which a chemical reaction proceeds.

(C) the rate at which a reaction proceeds.

(D) the feasibility of a chemical reaction.

Answer: the rate at which a reaction proceeds.

5. Choose the correct answer. A thermodynamic state function is a quantity

(A) used to determine heat changes

(B) whose value is independent of path

(C) used to determine pressure volume work

(D) whose value depends on temperature only.

Answer: whose value is independent of path

6. Which thermodynamic function accounts automatically for enthalpy and entropy both?

(A) Helmholtz Free Energy (A)

(B) Internal Energy (E)

(C) Work Function

(D) Gibbs Free Energy

Answer: Gibbs Free Energy

7. Which of the following statements is correct?

(A) The presence of reacting species in a covered beaker is an example of an open system.

(B) There is an exchange of energy as well as a matter between the system and the surroundings in a closed system.

(C) The presence of reactants in a closed vessel made up of copper is an example of a closed system.

(D) The presence of reactants in a thermos flask or any other closed insulated vessel is an example of a closed system.

Answer: The presence of reactants in a closed vessel made up of copper is an example of a closed system.

8. The entropy change can be calculated by using the expression ∆S = qrev/T When water freezes in a glass beaker, choose the correct statement amongst the following

(A) ∆S (system) decreases but ∆S (surroundings) remains the same.

(B) ∆S (system) increases but ∆S (surroundings) decreases.

(C) ∆S (system) decreases but ∆S (surroundings) increases.

(D) ∆S (system) decreases and ∆S (surroundings) also decreases.

Answer: ∆S (system) decreases but ∆S (surroundings) increases.

9. In an adiabatic process, no transfer of heat takes place between system and surroundings. Choose the correct option for free expansion of an ideal gas under adiabatic condition from the following.

(A) q = 0, ∆T ≠ 0, w = 0

(B) q ≠ 0, ∆T = 0, w = 0

(C) q = 0, ∆T = 0, w = 0

(D) q = 0, ∆T < 0, w ≠ 0

Answer: q = 0, ∆T = 0, w = 0

10. ∆fUᶱ of formation of CH4 (g) at certain temperature is –393 kJ mol–1. The value of ∆fHᶱ is

(A) zero

(B) < ∆f Uᶱ

(C) > ∆f Uᶱ

(D) equal to ∆f Uᶱ

Answer: < ∆f Uᶱ

11. The volume of gas is reduced to half from its original volume. The specific heat will be ______.

(A) reduce to half

(B) be doubled

(C) remain constant

(D) increase four times

12. The state of a gas can be described by quoting the relationship between___.

(A) pressure, volume, temperature

(B) temperature, amount, pressure

(C) the amount, volume, temperature

(D) pressure, volume, temperature, amount

Answer: pressure, volume, temperature, amount

13. The bond energy (in kcal mol-1) of a C-C single bond is approximately

(A) 1

(B) 10

(C) 83-85

(D) 1000

14. In which of the following process, a maximum increase in entropy is observed?

(A) Dissolution of Salt in Water

(B) Condensation of Water

(C) Sublimation of Naphthalene

(D) Melting of Ice

Answer: Sublimation of Naphthalene

15. An ideal gas is taken around the cycle ABCA as shown in P-V diagram The next work done by the gas during the cycle is equal to:

(A) 12P1V1

(B) 6P1V1

(C) 5P1V1

(D) P1V1

16. A system absorb 10 kJ of heat at constant volume and its temperature rises from 270 C to 370 C. The value of ∆ U is

(A) 100 kJ

(B) 10 kJ

(C) 0 kJ

(D) 1 kJ

17. The enthalpy of fusion of water is 1.435 kcal/mol. The molar entropy change for the melting of ice at 0°C is

(A) 5.260 cal/(mol K)

(B) 0.526 cal/(mol K)

(C) 10.52 cal/(mol K)

(D) 21.04 cal/(mol K)

Answer: 5.260 cal/(mol K)

18. Standard enthalpy of vapourisation DvapHQ for water at 100° C is 40.66 kJmol–1. The internal energy of vapourisation of water at 100°C (in kJmol–1) is

(A) +43.76

(B) +40.66

(C) +37.56

(D) –43.76

19. The standard enthalpy of formation (ΔfH°) at 298 K for methane, CH4(g), is –74.8 kJ mol–1. The additional information required to determine the average energy for C – H bond formation would be

(A) the dissociation energy of H2 and enthalpy of sublimation of carbon

(B) latent heat of vaporization of methane

(C) the first four ionization energies of carbon and electron gain enthalpy of hydrogen

(D) the dissociation energy of hydrogen molecule, H2

Answer: the dissociation energy of H2 and enthalpy of sublimation of carbon

20. An ideal gas is allowed to expand both reversibly and irreversibly in an isolated system. If Ti is the initial temperature and Tf is the final temperature, which of the following statements is correct?

(A) (Tf)irrev > (Tf)rev

(B) Tf > Ti for reversible process but Tf = Ti for irreversible process

(C) (Tf)rev = (Tf)irrev

(D) Tf = Ti for both reversible and irreversible processes

Answer: (Tf)irrev > (Tf)rev

21. Which of the following is an intensive property?

(A) temperature

(B) surface tension

(C) viscosity

(D) all of these

Answer: all of these

22. If one mole of ammonia and one mole of hydrogen chloride are mixed in a closed container to form ammonium chloride gas, then

(A) ΔH > Δu

(B) ΔH = Δu

(C) ΔH < Δu

(D) there is no relationship

Answer: ΔH < Δu

23. In a reversible process the system absorbs 600 kJ heat and performs 250 kJ work on the surroundings. What is the increase in the internal energy of the system?

(A) 850 kJ

(B) 600 kJ

(C) 350 kJ

(D) 250 kJ

24. The species which by definition has ZERO standard molar enthalpy of formation at 298 K is

(A) Br2(g)

(B) Cl2(g)

(C) H2O(g)

(D) CH4(g)

25. The enthalpy of vaporisation of a substance is 8400 J mol-1 and its boiling point is –173°C. The entropy change for vaporisation is:

(A) 84 J mol-1K-1

(B) 21 J mol-1K-1

(C) 49 J mol-1K-1

(D) 12 J mol-1K-1

Answer: 84 J mol-1K-1

26. One mole of which of the following has the highest entropy?

(A) Liquid Nitrogen

(B) Hydrogen Gas

(C) Mercury

(D) Diamond

27. For an ideal gas, the work of reversible expansion under isothermal condition can be calculated by using the expression w = – nRT ln Vf/Vi A sample containing 1.0 mol of an ideal gas is expanded isothermally and reversibly to ten times of its original volume, in two separate experiments. The expansion is carried out at 300 K and 600 K respectively. Choose the correct option.

A. Work done at 600 K is twice the work done at 300 K.

B. ∆U = 0 in both cases.

C. Both of these

D. None of these

28. The spontaneity means, having the potential to proceed without the assistance of an external agency. The processes which occur spontaneously are

(A) flow of heat from colder to warmer body.

(B) gas in a container contracting into one corner.

(C) gas expanding to fill the available volume.

(D) burning carbon in oxygen to give carbon dioxide.

29. In an exothermic reaction, heat is evolved, and the system loses heat to the surrounding. For such a system

(A) qp will be negative

(B) ∆rH will be negative

(C) qp will be positive

(D) ∆rH will be positive

30. In a constant volume calorimeter, 3.5 g of a gas with molecular weight 28 was burnt in excess oxygen at 298.0 K. The temperature of the calorimeter was found to increase from 298.0 K to 298.45 K due to the combustion process. Given that the heat capacity of the calorimeter is 2.5 kJ K−1, the numerical value for the enthalpy of combustion of the gas in kJ mol−1 is

(A) 3

(B) 7

(C) 8

(D) 9

31. The amount of heat evolved when 500 cm3 of 0.1 M HCl is mixed with 200 cm3 of 0.2 M NaOH is ______.

(A) 1.292 kJ

(B) 2.292 kJ

(C) 3.392 kJ

(D) 0.292 kJ

32. The standard enthalpy of formation of NH3 is –46.0 kJ mol–1. If the enthalpy of formation of H2 from its atoms is –436 kJ mol–1 and that of N2 is –712 kJ mol–1, the average bond enthalpy of N — H bond is NH3 is

(A) –1102 kJ mol–1

(B) –964 kJ mol–1

(C) +352 kJ mol–1

(D) +1056 kJ mol–1

Answer: +352 kJ mol–1

33. The species which by definition has ZERO standard molar enthalpy of formation at 298 K is

(A) Br2(g)

(B) Cl2(g)

(C) H2O(g)

(D) CH4(g)

34. The bond energy (in kcal mol–1) of a C—C single bond is approximately

(A) 1

(B) 10

(C) 100

(D) 1000

35. The amount of the heat released when 20 ml 0.5 M NaOH is mixed with 100 ml 0.1 M HCl is x kJ. The heat of neutralization is

(A) – 100 x kJ/mol

(B) – 50 x kJ/mol

(C) + 100 x kJ/mol

(D) +50 x kJ/mol

Answer: – 100 x kJ/mol

36. Standard enthalpy of vapourisation ΔHvap for water at 100oC is 40.66 kJmol-1. The internal energy of vapourisation of water at 100°C (in kJmol-1) is (Assume water vapour to behave like an ideal gas)

(A) 43.76

(B) 40.66

(C) 37.56

(D) -43.76

37. Which of the following salts will have maximum cooling effect when 0.5 mole of the salt is dissolved in same amount of water. Integral heat of solution at 298 K is given for each salt?

(A) KNO3 (∆H = 35.4 kJ mol-1)

(B) NaCl (∆H = 5.35 kJ mol-1)

(C) HBr (∆H = -83.3 kJ mol-1)

(D) KOH ( ∆H = -55.6 kJ mol-1)

Answer: KNO3 (∆H = 35.4 kJ mol-1)

38. The temperature of the system decreases in an ______.

(B) Isothermal Expansion

(C) Isothermal Compression

39. A system absorb 10 kJ of heat at constant volume and its temperature rises from 270°C to 370°C. The value of ∆ U is

(A) 100 kJ

(B) 10 kJ

(C) 0 kJ

(D) 1 kJ

40. The amount of the heat released when 20 ml 0.5 M NaOH is mixed with 100 ml 0.1 M HCl is x kJ. The heat of neutralization is

(A) -100 × kJ/mol

(B) -50 × kJ/mol

(C) 100 × KJ/mol

(D) 50 × kJ/mol

Answer: -100 × kJ/mol

41. The enthalpies of combustion of carbon and carbon monoxide are -393.5 and -283.0 kJ mol-1 respectively. The enthalpy of formation of carbon monoxide is:

(A) -676 kJ

(B) 110.5 kJ

(C) -110.5 kJ

(D) 676.5 kJ

42. Which of the following is not correct?

(A) ∆G is zero for a reversible reaction

(B) ∆G is positive for a spontaneous reaction

(C) ∆G is negative for a spontaneous reaction

(D) ∆G is positive for a non-spontaneous reaction

Answer: ∆G is positive for a spontaneous reaction

43. Enthalpy of sublimation of a substance is equal to

(A) enthalpy of fusion + enthalpy of vapourisation

(B) enthalpy of fusion

(C) enthalpy of vapourisation

(D) twice the enthalpy of vapourisation

Answer: enthalpy of fusion + enthalpy of vapourisation

44. The enthalpies of elements in their standard states are taken as zero. The enthalpy of formation of a compound

(A) is always negative

(B) is always positive

(C) maybe positive or negative

(D) is never negative

Answer: maybe positive or negative

45. The temperature of the system .decreases in an ______.

(B) isothermal expansion

(C) isothermal compression

46. In a system where ∆E = -51.0 kJ, a piston expanded against a pext of 1.2 atm giving a change in volume of 32.0 L. What was the change in heat of this system?

(A) -36 kJ

(B) -13 kJ

(C) -47 kJ

(D) 24 kJ

47. Calculate the heat required to make 6.4 Kg CaC2 from CaO(s) and C(s) from the reaction: CaO(s) + 3 C(s) → CaC2(s) + CO (g) given that ∆f Ho (CaC2) = -14.2 kcal. ∆f H° (CO) = -26.4 kcal.

(A) 5624 kcal

(B) 1.11 × 104 kcal

(C) 86.24 × 10³

(D) 1100 kcal

Answer: 1.11 × 104 kcal

48. Which of the following is true for the reaction? H2O (l) ↔ H2O (g) at 100° C and 1 atm pressure

(A) ∆S = 0

(B) ∆H = T ∆S

(C) ∆H = ∆U

(D) ∆H = 0

Answer: ∆S = 0

49. For the process to occur under adiabatic conditions, the correct condition is

(A) ΔT = 0

(B) Δp = 0

(C) g = 0

(D) w=0

Answer: g = 0

50. The enthalpies of all elements in their standard states are

(A) unity

(B) zero

(C) <0

(D) different for each element.