CBSE Class 11 Chemistry Thermodynamics MCQs Set E

Question. A hypothetical reaction A ➔ 2B, proceeds through following sequence of steps
(i) A → C; ΔH = q
(ii) C → D; ΔH = V
(iii) 1/2 D → B; ΔH = x
Then, the heat of reaction is 
(a) q – v + 2x
(b) q + v – 2x
(c) q + v + 2x
(d) q + 2v – 2x
Answer: c

Question. In a closed contamer, 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
Answer: a

Question. Two moles of helium gas expanded isothermally and irreversible at 27°C fom1 volume 1 dm³ to 1 m³ at constant pressure of 100 k Pa. Calculate the work done. 
(a) 99900 kJ
(b) 99900 J
(c) 35464.65 kJ
(d) 34465.65 J 
Answer: b

Question. When one mole of monoatomic ideal gas at TK undergoes adiabatic change under a constant external pressure of 1 atm changes volume from 1 L to 2 L. The final temperature in Kelvin would be 
(a) T/2^2/3
(b) T + 2/3x 0.0821
(c) T
(d) T + 2/3 X 0.082
Answer: a

Question. When two moles of hydrogen expands isothem1aJly against a constant pressure of 1 atm, at 25° C from 15 L to 50 L, the work done (in litre atrn) will be
(a) 17.5
(b) 35
(c) 51.5
(d) 70
Answer: b

Question. For the complete combustion of ethanol, C₂H₅OH (/) + 3O₂ (g) → 2CO₂ (g) + 3H₂O(/) the amount of beat produced as measured in bomb calorimeter, is 1364.4 7 kJ mol^-1 at 25°C. Assuming ideality the enthalpy of combustion, ΔH_c, for the reaction will be (R = 8.314JK^-1 mol^-1) 
(a) -1366.95 kJ mol^-1
(b) -1361.95 kJ mol^-1
(c) -1460.50 kJ mol^-1
(d) – 1350.50 kJ mol^-1
Answer: a

Question. The heat of combustion of sucrose, C₁₂H₂₂O₁₁ (s) at constant volume is 1348.9 kcal mol^-1 at 25°C, then the heat of reaction at constant pressure when steam is produced 
(a) – 1348.9 kcal
(b) -1342.34 kcal
(c) + 1250 kcal
(d) None of the above
Answer: b

Question. The standard molar beat of formation of ethane, CO₂ and water (l) are respectively – 21 .1, – 94.1 and – 68.3 kcal. The standard molar heat of combustion of ethane will be
(a) – 372 kcal
(b) 162 kcal 
(c) – 240 kcal
(d) 183.5 kcal
Answer: a

Question. The ratio of heats liberated at 298 K from the combustion of one kg of coke and by burning water gas obtained from 1 kg of coke is (Assume coke to be 100% carbon). (Given : enthalpies of combustion of C, CO and H₂ as 393.5 kJ, 285 kJ, 285 kJ respectively all at 298 K)
(a) 0.79: 1
(b) 0.69: 1
(c) 0.86: 1
(d) 0.96: 1
Answer: b

Question. In order to decompose 9 g water 142.5 kJ heat is required. Hence, the enthalpy of fom1ation of water is 
(a) –142.5 kJ
(b) + 142.5 kJ
(c) –285 kJ
(d) + 285 kJ
Answer: c

Question. The enthalpy of combustion of C₆H₆ (/) is – 3250 kJ. When 0.39 g of benzene is burnt in excess of oxygen in an open vessel, the amount of heat liberated is 
(a) 16.25 J
(b) 16.25 kJ
(c) 32.5 J
(d) 32.5 kJ
Answer: b

Question. A coffee cup calorimeter initially contains 125 g of water at a temperature of 24.2°C. After adding 10.5 g of KBr, the temperature becomes 21.1°C. The heat of solution is
(a) 40 J/g
(b) 117 J/g 
(c) 167.7 J/g
(d) 420.05 J/g
Answer: c

Question. Given, that,
H₂O(/) → H⁺ (aq)+ OH^– (aq); ΔH = 57.32 kJ
H2 (g) + 1/2O2 (g) → H₂ O(/); ΔH = –286.02 kJ
Then, calculate the enthalpy of fonnation of OH- at 25°C.
(a) –228.8 kJ
(b) –343.53 kJ 
(c) + 228.8 kJ
(d) + 343.52 kJ
Answer: a

Question. Calculate the amount of heat evolved when 500cm³ of 0.1 M HCl ismixed with 200cm³ of 0.2 MNaOH.
(a) 57.3 kJ
(b) 2.865 kJ 
(c) 2.292 kJ
(d) 0.573 kJ
Answer: c

Question. A sample of liquid in a thermally insulated container is stirred for 1 h by a mechanical attachment to a motor in the surroundings, which of the following thennodynarnic quantity for the system is zero ?
(a) Work (W)
(b) Change in internal energy (ΔE)
(c) Change in enthalpy (ΔH)
(d) None of the above
Answer: d

Question. The value of enthalpy change (ΔH) for the reaction C₂H₅OH (/)+ 3O₂ (g )➔ 2CO₂ (g )+ 3H₂O(l),at 27°C is -1366. 5kJ mol^-1 The value ofintemal energy change for the above reaction at this temperature will be 
(a) – 1371.5 kJ
(b) – 1369.0kJ
(c) -1364.0kJ
(d) -1361.SkJ
Answer: c

Question. Consider the reaction,
4NO₂ (g)+ O₂ (g) → 2N₂O₅ (g), Δ_rH = -Ill KJ. If N₂O₅5 ( s) is fonned instead of N₂O₅ (g) in the above reaction, the Δ_rH value will be (Given, Aff of sublimation for N₂O₅ is 54 kJ mol^–1) 
(a) – 165kJ
(b) + 54kJ
(c) + 219k
(d) – 219kJ
Answer: d

Question. Molar heat capacity of aluminium is 25 JK^-1 mol^-1 • The heat necessary to raise the temperature of 54 g of aluminium (Atomic mass 27 g mol^-1) from 30°C to 50°C is 
(a) 1.5kJ
(b) 0.5 kJ
(c) l.0kJ
(d) 2.5kJ
Answer: c

Question. The amount of the heat released when 20 mL 0. 5 M NaOH is mixed with 100 mL 0.1 M HCI is x kJ The heat of neutralisation is
(a) -l00x kJ/mol
(b) -50x kJ/mol
(c) +l00x kJ/mol
(d) +50x kJ/ mol
Answer: a

Question. The bond energy (in kcal mol^-1) of C—C single bond is approxin1ately 
(a) 1 
(b) 10
(c) 100
(d) 1000
Answer: c

Question. 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)
Answer: b

Question. 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-Hbond in NH₃ is 
(a) -964 kJ mol^-1
(b) + 352 kJ mol^-1
(c) + 1056 kJ mol^-1
(d) -1102 kJ mol^-1
Answer: b

Question. In which of the following reactions, the enthalpy is the least ? 
(a) CH₃COOH + NaOH → CH₃COONa + H₂O
(b) HCl+ NH₄OH → NH₄Cl + H₂O
(c) HCI + NaOH → NaCl + H₂O
(d) HCN+ NH₄OH → NH₄CN + H₂O
Answer: d

Question. The enthalpy of formation of NH₃ is-46kJ mol^-1. The enthalpy change for the reaction
2NH₃ (g ) ➔ N₂ (g )+ 3H₂ (g) is 
(a) + 184 kJ
(b) + 23 kJ
(c) + 92 kJ
(d) + 46 kJ
Answer: c

Question. For the reactions A ➔ B; ΔH = + 24 kJ/mol and B ➔ C; ΔH = -18 kJ/mol, the decreasing order of
enthalpy of A, B, C follows the order 
(a) A,B,C
(b) B,C,A
(c) C,B,A
(d) C,A,B
Answer: b

Question. Calculate LVf in kJ for the following reaction
C(g)+ O₂(g) → CO₂ (g)
Given that,
H₂O(g) + C(g) → CO(g)+ H₂ (g); ΔH = + 131 kJ
CO(g)+ 1/2 O₂(g) → CO₂ (g); ΔH= -282kJ
H₂ (g)+ 1/2 O2(g) → H₂O (g); ΔH = -242 kJ
(a) -393
(b) + 393 
(c) + 655
(d) -655
Answer: a

Question. The heat of combustion of solid benzoic acid at constant volume is -321. 30 kJ at 27° C. The heat ofcombustion at constant pressure is
(a) – 321.30 – 300R
(b) – 321.30 + 300 R
(c) – 321.30-150R
(d) – 321.30+ 900 R
Answer: c

Question. Which of the following reaction defines ΔH°_f ?
(a) C(diamond) + O₂ (g) → CO₂ (g) 
(b) 1/2 H₂ (g) + 2F₂(g) → HF(g)
(c) N₂(g) + 3H₂(g) → 2NH₃ (g) 
(d) CO(g) + 1/2 O₂(g) → CO₂ (g)
Answer: b

Question. Using the following thermochemical equations
(i) S(rhombic) + 1/2 O₂ (g) → SO₃ (g);
ΔH = -2x kJ mol^-1
(ii) SO₂ (g)+ 1/2 O₂ (g) → SO₃ (g);
ΔH = – y kl mol^-1
Find out the heat of fom1ation of SO₂ (g) in kJ mol^-1
(a) (2x+ y)
(b) (x + y) 
(c) (2x/y)
(d) (y – 2x)
Answer: d

Question. The heat of formations for CO₂ (g ), H₂O (l) and CH₄ (g) are – 400 kJ mol^-1, – 280 kJ mol^-1 and – 70 kJ mol^-1 respectively. The heat of combustion of CH₄ in kJ mol^-1 is
(a) 890
(b) – 160 
(c) – 890
(d) – 90
Answer: c

Question. The bond dissociation energies of H₂ , Cl₂ and HCl are 104, 58 and 103 kcal mol^-1 respectively. The enthalpy of fom1ation of HCl would be 
(a) – 22 kcal mol^-1
(b) – 44 kcal mol^-1
(c) + 44 kcal mol^-1
(d) + 22kcal mol^-1
Answer: a

Question. Given, 2C + 2O₂ (g) → 2CO₂ (g); ΔH = -787 kJ
H₂(g)+ 1/2 O₂(g) → H₂O(/); ΔH = – 286 kJ
C₂H₂(g)+ 1/2 O₂(g) → 2C₂(g) + H₂O(/)
ΔH = -1310kJ
The heat of formation of acetylene is 
(a) – 1802 kJ
(b) + 1802 kJ
(c) + 237 kJ
(d) – 800 kJ
Answer: c