CBSE Class 11 Chemistry Thermodynamics Assignment

Question. The internal energy change when a system goes from state A to B is 40 kJ/mol. If the system goes from A to B by a reversible path and returns to state A by an irreversible path what would be the net change in internal energy ?
(a) > 40 kJ
(b) < 40 kJ
(c) Zero
(d) 40 kJ
Answer : C

Question. A gas absorbs 200 J heat and undergoes simultaneous expansion against a constant external pressure of 10⁵ Pa. The volume changes  from 4L to 5L. The change in internal energy is
(a) 300 J
(b) 100 J
(c) –300 J
(d) – 100 J
Answer : B

Question. When 110 g of manganese (At. mass = 55) dissolves in dilute HNO₃ at 27°C under atmospheric pressure, the work done in the process is :
(a) 2494.2 J
(b) – 2494.2 J
(c) – 4988.4 J
(d) 4988.4 J
Answer : C

Question. Workdone for the conversion of 0.5 mole of water at 100ºC to steam at 1 atm pressure is (heat of vaporisation of water at 100ºC is 40670 J mol^–1)
(a) –1.54 kJ
(b) 1.54 kJ
(c) 1.25 kJ
(d) –1.35 kJ
Answer : A

Question. The amount of work done by 2 mole of an ideal gas at 298 K in reversible isothermal expansion from 10 litre to 20 litre will be
(a) 3.4 kJ
(b) –3.4 kJ
(c) 4.0 kJ
(d) –4.0 kJ
Answer : B

Question. The enthalpy changes for the following processes are listed below :
Cl₂(g) → 2Cl(g), 242.3 kJ mol^–1
I₂(g) → 2I(g), 151.0 kJ mol^–1
ICl(g) → I(g) + Cl(g), 211.3 kJ mol^–1
I₂(s) → I₂(g), 62.76 kJ mol^–1
Given that the standard states for iodine and chlorine are I₂(s) and Cl₂(g), the standard enthalpy of formation for ICl(g) is :
(a) +16.8 kJ mol^–1
(b) +244.8 kJmol^–1
(c) –14.6 kJ mol^–1
(d) –16.8 kJ mol^–1
Answer : A

Question. The quantity of heat (in J) required to raise the temperature of 1.0 kg of ethanol from 293.45 K to the boiling point and then change to liquid to vapour at that temperature is closest to [Given, boiling point of ethanol 351.45 K. Specific heat capacity of liquid ethanol 2.44 J g^–1 k^–1. Latent heat of vaporisation of ethanol 855 J g^–1]
(a) 142 × 10²
(b) 9.97 × 10²
(c) 142 × 10⁵
(d) 9.97 × 10⁵
Answer : D

Question. Oxidising power of chlorine in aqueous solution can be determined by the parameters indicated below:

Δeg H Cl = –349 kJ mol^–1
Δhyd HCl– = –381 kJ mol^–1, will be
(a) + 152 kJ mol^–1
(b) – 850 kJ mol^–1
(c) – 610 kJmol^–1
(d) + 120 kJ mol^–1
Answer : C

Question. A gas expands reversibly from state A to state B by three paths 1, 2 and 3 as shown in the figure. If w₁, w₂ and w₃ respectively be the work done by the gas along three paths then

(a) w₁ > w₂ > w₃
(b) w₁ < w₂ < w₃
(c) w₁ = w₂ = w₃
(d) w₂ < w₃ < w₁
Answer : B

Question. 10 mole of an ideal gas expand isothermally and reversibly from a pressure of 10 atm to 1atm at 300 K. What is the largest mass which can lifted through a height of 100 meter?
(a) 31842 kg
(b) 58.55 kg
(c) 342.58 kg
(d) 6051 kg
Answer : B

Question. Given that C + O₂ → CO₂ : ΔHº = - x kJ
2CO + O₂ → 2CO₂ : ΔHº = - y kJ
the enthalpy of formation of carbon monoxide will be
(a) 2x - y/2
(b) y-2x/2
(c) 2x – y
(d) y – 2x
Answer : B

Question. One mole of CH₃COOH undergoes dimerization in vapour phase at 127°C as:
2CH COOH (g) ⇔ (CH COOH)₂ (g) if dimer formation is due to two H-bonds involved in dimer, each of 33 kJ stength and the degree of dimerisation of acetic acid 98.2%. The change in standard entropy during dimerization is
(a) –104 JK^–1 mol^–1
(b) –120 JK^–1 mol^–1
(c) 135 JK^–1 mol^–1
(d) 108 JK^–1mol^–1
Answer : A

Question. Given that the molar combustion enthalpy of benzene, cyclohexane, and hydrogen are x, y, and z, respectively, the molar enthalpy of hydrogenation of benzene to cyclohexane is
(a) x - y + z
(b) x - y + 3z
(c) y - x + z
(d) y - x + 3z
Answer : B

Question. For vaporization of water at 1 atmospheric pressure, the values of ΔH and ΔS are 40.63 kJmol^–1 and 108.8 JK^–1 mol^–1, respectively. The temperature when Gibbs energy change (ΔG) for this transformation will be zero, is:
(a) 293.4 K
(b) 273.4 K
(c) 393.4 K
(d) 373.4 K.
Answer : D

Question. The specific heat of a monoatomic gas at constant pressure is 248.2 J kg^–1 K^–1 and at constant volume it is 149.0 J kg^–1 K^–1. The mean molar mass of the gas is
(a) 83.8 g mol^–1
(b) 84.0 g mol^–1
(c) 82 g mol^–1
(d) 80 g mol^–1
Answer : A

Question. For a spontaneous process
(a) enthalpy change of the system must be negative.
(b) entropy change of the system must be positive.
(c) entropy change of the surrounding must be positive.
(d) entropy change of the system plus surrounding must be positive.
Answer : D

Question. At the sublimation temperature, for the process CO₂(s) ⇔ CO₂(g)
(a) ΔH, ΔS and ΔG are all positive
(b) ΔH > 0, ΔS > 0 and ΔG < 0
(c) ΔH < 0, ΔS > 0 and ΔG < 0
(d) ΔH > 0, ΔS > 0 and ΔG = 0
Answer : D

Question. The factor of ΔG values is important in metallurgy. The ΔG values for the following
reactions at 800ºC are given as :
S₂ (s)+ 2O₂ (g) → 2SO₂ (g) ; ΔG = – 544 kJ
2Zn(s)+ S₂ (s) → 2ZnS(s) ; ΔG = – 293 kJ
2Zn(s)+ O₂ (g) → 2ZnO(s) ; ΔG = – 480 kJ
Then ΔG for the reaction :
2ZnS(s) + 3O₂ (g) → 2ZnO(s) + 2SO₂ (g) will be :
(a) –357 kJ
(b) –731 kJ
(c) –773 kJ
(d) –229 kJ
Answer : B

Question. The values of standard enthalpy of formation of SF6(g), S(g)and F(g) are : – 1100, 275 and 80 kJ mol^–1 respectively. The average S–F bond energy in SF₆ will be
(a) 309 kJ
(b) 315 kJ
(c) 320 kJ
(d) 300 kJ
Answer : A

Question. Given the following entropy values (in J K^–1 mol^–1) at 298 K and 1 atm :H₂(g) : 130.6, Cl₂(g) : 223.0, HCl(g) : 186.7.The entropy change (in J K^–1 mol^–1) for the reaction H₂ (g) + Cl 2 (g) → 2HCl (g) is
(a) +540.3
(b) +727.0
(c) –166.9
(d) +19.8
Answer : D

Numeric Value Answer

Question. For a dimerization reaction, 2A(g) → A₂ (g), at 298 K,ΔU^Θ = -20 kJ mol^–1, ΔS^Θ = -30  K^–1 mol^–1, then the ΔG^Θ will be ___________ J.
Answer : –13538

Question. The magnitude of work done by a gas that undergoes a reversible expansion along the path ABC shown in the figure is _______

Answer : 48.00

Question. At constant volume, 4 mol of an ideal gas when  heated from 300 K to 500 K changes its internal energy by 5000 J. The molar heat capacity at constant volume is ______.
Answer : 6.25

Question. A perfect gas undergoes a reversible adiabatic expansion from (300 K, 200 atm) to (90 K, 10 atm). The atomicity of gas will be
Answer : 1

Question. A mixture of ferric oxide, Fe₂O₃, and aluminium, Al, is used in solid fuel rockets. The fuel value per cc of the mixture is
Heats of formation and densities are as follows :
Hf (Al₂O₃) = 399 kcal/mol;
Hf (Fe₂O₃) = 199 kcal/mol;
Density of Fe₂O₃ = 5.2 g/cc;
Density of Al = 2.7 g/cc.
Answer : 4

Question. x g sample of NH₄NO₃ is decomposed in a Bomb calorimeter. The temperature of calorimeter
increase by 4°C. The heat capacity of the system is 125 kJ/°C. The value of x is (Given molar heat of decomposition of NH₄NO₃ at constant volume is 400 kJ mol^–1)
Answer : 1

Question. A heat engine is operating between 500K to 400K. If the engine absorbs 100 J heat, the impossible amount of heat rejected by the engine is 20TJ, then the value of T is ________
Answer : 4

Question. One mole of a real gas undergoes a change of state A to B with a change in internal energy

ΔE = 50 L – atm. What is the value of change in enthalpy in L – atm?
Answer : 76

Question. A 20g piece of iron (specific heat capacity = 0.5 J/g °C) at 200°C is immersed in 100g water of 27°C. What will be the temperature (°C) of this system at thermal equilibrium?
Answer : 31

Question. Nitroglycerine (MW = 227.1) detonated according to the following equations, 2C3H₅(NO₃)₃(l) → 3N₂(g) + 1/2 O₂(g) + 6CO₂(g) + 5H₂O(g)
The standard molar enthalpies of formation,
ΔH⁰f for all the compounds are given below.
ΔH°f [C₃H₅(NO₃)₃] = – 364 kJ/mol
ΔH°f [CO₂(g)] = – 393.5 kJ/mol
ΔH°f [H2O(g)] = – 241.8 kJ/mol
ΔH°f [N₂(g)] = 0 kJ/mol
ΔH°f [O₂(g)] = 0 kJ/mol
The enthalpy change when 10 g of nitroglycerine is detonated as
Answer : 62.5

1. Thermodynamics: Science which deals with study of different forms of energy and quantitative relationship.

2. System & Surroundings: The part of universe for study is called system and remaining portion is surroundings.

3. State of system & state function: State of system is described in terms of T, P, V etc. The property which depends only on state of system not upon path is called state function eg. P, V, T, E, H, S etc.

4. Extensive & Intensive Properties: Properties which depends on quantity of matter called extensive prop. eg. mass, volume, heat capacity, enthalpy, entropy etc. The properties which do not depends on matter present depends upon nature of substance called Intensive properties. eg. T,P, density, refractive index, viscosity, bp, pH, mole fraction etc.

5. Internal energy: The total energy with a system.

i.e. U = E_e + E_n + E_c + E_p + E_k + ------

U = U₂ – U₁ or U_P – U_R & U is state function and extensive properly. If U₁ > U₂ energy is released.

6. Heat (q): It I a form of energy which is exchanged between system and surrounding due to difference of temperature. Unit is Joule (J) or Calorie (1Calorie = 4.18 J).

7. First Law of Thermodynamics: It is law of conservation energy. Energy can neither be created not destroyed, it may be converted from one from into another.

Mathematically U = q + w, w = –p. V (work of expansion)

U = q – p. V or q = U + p. V, q,w are not state function.

But U is state function.

8. Enthalpy (H): At constant volume V = 0, qv = U So H = U + p. V, qp = H² H¹ = H H = U + P. V.

9. Relationship between qp, qv i.e. H& U It is H = U+ ng.RT or q^p = q^v + ng.RT

10. Exothermic and Endothermic reactions: H = –Ve for exothermic and H

= +Ve for endothermic reaction i.e. evolution and absorption of heat.

Eg C+O² → CO² + 393.5 KJ, H = –393.5 KJ (exothermic)

N² + O² → 2NO – 180.7 KJ, H = 180.7 KJ (Endothermic)

11. Enthalpy of reaction ( rH): The amount of heat evolved or absorbed when the reaction is completed.

12. Standard Enthalpy of reaction ( rH0) at 1 bar pressure and specific temp.

ONE MARK QUESTIONS

1. Dissolution of ammonium chloride in water is endothermic yet it is a spontaneous process. Explain

2. When will heat change at constant volume and heat change at constant pressure be equal?

3. Discuss the role of temperature in determining the spontaneity of a process.

4. Give two examples of state functions.

5. Predict the change in internal energy for an isolated system at constant volume.

TWO MARK QUESTIONS

1. Derive the relationship between Cp and Cv

2. State

i. Hess’s law of constant heat summation

ii. Second law of thermodynamics

3. Derive the relation ΔH = ΔU + Δn_gRT

4. What will be the sign of entropy change for the following changes?
a) In an isolated system, two identical gases are allowed to mix under identical conditions.
b) I₂(g) → I2(s)
c) H₂(g) + I₂(g) → 2HI(g)
d) Dissolution of sugar in water contained in a thermos flask.

5 ΔH and ΔS for the reaction Ag₂O ⇌ 2Ag + ½ O₂ are 30.56 KJ/mole and 60 J/K respectively. Calculate the temperature at which the free energy change for this reaction will be zero. Predict whether the forward reaction will be favoured above/below this T.

6 Calculate the Kc at 298 K for the reaction H₂ + I₂ ⇌ 2HI, if ΔG^of (HI) = 1.3kJ/mole

7 Differentiate between
a) heat of formation and heat of reaction
b) heat of hydration and heat of solution

8 Calculate heat change at constant pressure if heat change at constant volume for the reaction NH₂CN(g) + 3/2 O₂(g) → N2(g) + CO₂(g) + H₂O(l) at 298K is -742 kJ/mole

9 What would be the work done when the pressure of 2 moles of an ideal gas is changed from 2 bar to 5 bar isothermally and reversibly at 25^oC ?

THREE MARK QUESTIONS

1 Define
(i) Molar heat capacity (ii) Enthalpy of a reaction (iii) Residual entropy

2 Comment on the following statements
(i) An exothermic reaction is always thermodynamically spontaneous.
(ii) The entropy of a substance increases when going from liquid state to vapour state at any temperature.
(iii) A reaction with ΔG0 >0 always has an equilibrium constant greater than one

3 (i) For the equilibrium PCl₅ ⇌ PCl₃ + Cl₂ at 25 ⁰C, K = 1.8 x 10^-7. Calculate ΔG^o of reaction
(ii) For the reaction 2NO (g) + O₂(g) ⇌ 2NO₂(g), calculate the ΔG at 600 K if enthalpy and entropy changes are –110kJ/mole and 150 J/Kmole

4 For the synthesis of NH₃ ,N₂(g) + 3H₂(g)⇌ 2NH₃(g), calculate Kp at 300K if ΔH^of of

5 NH₃ as -46.2 kJ/mole and ΔS^o for the reaction is 198.3 J/Kmole.
(i) The ΔH_vap of water at 100^oC is 41kJ/mole. Calculate the internal energy change.
(ii) What is the work done on a gas when 10 lt of the gas is compressed to 4.5 lt under a constant pressure of 103kPa?

6 Calculate the ΔH⁰f of benzene if ΔH_comb of benzene, carbon and hydrogen are 3267, 393 and 286 kJ/mole respectively.

7 The mean bond enthalpies of N≡N and H-H are 946 and 436 kJ/mole respectively. If heat of formation of ammonia is -46kJ/mole, calculate the mean BE of N-H bonds in ammonia.

8 (i) Calculate the entropy change in surroundings when 36 g of water is formed under standard conditions. ΔH⁰f of water = -286kJ/mole
(ii) Calculate the work done when 2.5 moles of an ideal gas at 300K is isothermally and reversibly compressed from a volume of 5m3 to a volume of 2 m³