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Chemical Thermodynamics

JEE Mains Chemistry. Try each one first, then open its answer.

Top 10 JEE Mains PYQs to practise first

The questions and kinds of question asked most often come first. Each one says how often and in which papers.

  1. Question 1

    This type asked 7 times: 14 Jun 2022, 25 Jun 2022, 25 Jul 2022, 6 Apr 2023, 22 Jan 2025, 28 Jan 2025, 4 Apr 2026 S2. This one: 4 Apr 2026 S2 See all 7 of this type

    46
    If 3.365 g of ethanol ( ll ) burnt completely in a bomb calorimeter at 298.15 K , the heat produced is 99.472 kJ . The ∣ΔHf ∘∣\left| \Delta H_{f}\ ^{\circ} \right| of ethanol at 298.15 K is ____\_\_\_\_ kJ mol−1kJ{\text{ }mol}^{- 1}. (Nearest integer) Given : Standard enthalpy of combustion of graphite =−393.5 kJ mol−1= - 393.5\text{ }kJ{\text{ }mol}^{- 1} Standard enthalpy of formation of water ( ll )=−285.8 kJ mol−1= - 285.8\text{ }kJ{\text{ }mol}^{- 1}. Molar mass in gmol−1{gmol}^{- 1} of C,H,OC,H,O are 12,1 and 16 respectively.

  2. Question 2

    This type asked 5 times: 2021 Paper 21, 2021 Paper 25, 25 Jun 2022, 6 Apr 2024, 24 Jan 2025. This one: 24 Jan 2025 See all 5 of this type

    47
    Standard entropies of X2,Y2X_{2},Y_{2} and XY5XY_{5} are 70,50 and 110 J K−1 mol−1110\text{ }J{\text{ }K}^{- 1}{\text{ }mol}^{- 1} respectively. The temperature in Kelvin at which the reaction
    12X2+52Y2→XY5ΔH⊖=−35 kJ mol−1\frac{1}{2}X_{2}+\frac{5}{2}Y_{2}\rightarrow XY_{5}\quad \Delta H^{\ominus}= - 35\text{ }kJ{\text{ }mol}^{- 1}
    will be at equilibrium is _______\_\_\_\_\_\_\_ (Nearest integer)

  3. Question 3

    This type asked 5 times: 26 Jun 2022, 28 Jun 2022, 26 Jul 2022, 8 Apr 2023, 5 Apr 2024. This one: 5 Apr 2024 See all 5 of this type

    53
    The heat of combustion of solid benzoic acid at constant volume is −321.30 kJ- 321.30\text{ }kJ at 27∘C27^{\circ}C. The heat of combustion at constant pressure is (−321.30−xR)( - 321.30 - xR) kJkJ, the value of xx is ______

  4. Question 4

    This type asked 4 times: 11 Apr 2023, 30 Jan 2024, 5 Apr 2024, 8 Apr 2026 S2. This one: 8 Apr 2026 S2 See all 4 of this type

    49
    Consider the reaction :
    2H2 S( g)+3O2( g)→2H2O(l)+2SO2( g)2H_{2}\text{ }S(\text{ }g) + 3O_{2}(\text{ }g) \rightarrow 2H_{2}O(l) + 2{SO}_{2}(\text{ }g)
    The magnitude of enthalpy change for the reaction in kJmol−1kJ{mol}^{- 1} is ____\_\_\_\_ . (Nearest integer) Given : ΔfH⊖(H2 S)=−20.1 kJ mol−1\Delta_{f}H^{\ominus}\left( H_{2}\text{ }S \right) = - 20.1\text{ }kJ{\text{ }mol}^{- 1}
    ΔfHΘ(H2O)=−286.0 kJ mol−1\Delta_{f}H^{\Theta}\left( H_{2}O \right) = - 286.0\text{ }kJ{\text{ }mol}^{- 1}
    ΔfHΘ(SO2)=−297.0 kJ mol−1\Delta_{f}H^{\Theta}\left( {SO}_{2} \right) = - 297.0\text{ }kJ{\text{ }mol}^{- 1}

  5. Question 5

    This type asked 4 times: 6 Apr 2023, 27 Jan 2024, 21 Jan 2026 S1, 6 Apr 2026 S1. This one: 6 Apr 2026 S1 See all 4 of this type

    50
    Consider the reaction X⇌YX \rightleftharpoons Y at 300 K . If ΔHθ\Delta H^{\theta} and K are 28.40 kJ mol−128.40\text{ }kJ{\text{ }mol}^{- 1} and 1.8×10−71.8 \times 10^{- 7} at the same temperature, then the magnitude of ΔSθ\Delta S^{\theta} for the reaction in JK−1 mol−1JK^{- 1}{\text{ }mol}^{- 1} is ____\_\_\_\_ .(Nearest Integer). (Given : R=8.3JK−1 mol−1,ln⁡10=2.3R = 8.3{JK}^{- 1}{\text{ }mol}^{- 1},\ln10 = 2.3, log⁡3=0.48,log⁡2=0.30\log3 = 0.48,\log2 = 0.30

  6. Question 6

    This type asked 4 times: 27 Jun 2022, 31 Jan 2024, 4 Apr 2025, 28 Jan 2026 S1. This one: 28 Jan 2026 S1 See all 4 of this type

    26
    20.0dm320.0dm^{3} of an ideal gas ' X ' at 600 K and 0.5 MPa undergoes isothermal reversible expansion until pressure of the gas is 0.2 MPa . Which of the following option is correct? (Given: log⁡2=0.3010\log2 = 0.3010 and log⁡5=0.6989\log5 = 0.6989 )

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  7. Question 7

    This type asked 4 times: 24 Jan 2023, 23 Jan 2025, 24 Jan 2025, 4 Apr 2025. This one: 4 Apr 2025 See all 4 of this type

    27
    Let us consider a reversible reaction at temperature, T . In this reaction, both ΔH\Delta H and ΔS\Delta S were observed to have positive values. If the equilibrium temperature is Te , then the reaction becomes spontaneous at :

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  8. Question 8

    This type asked 4 times: 26 Jul 2022, 27 Jul 2022, 1 Feb 2023, 3 Apr 2025. This one: 3 Apr 2025 See all 4 of this type

    123
    A sample of n-octane (1.14 g)(1.14\text{ }g) was completely burnt in excess of oxygen in a bomb calorimeter, whose heat capacity is 5 kJ K−15\text{ }kJ{\text{ }K}^{- 1}. As a result of combustion reaction, the temperature of the calorimeter is increased by 5 K . The magnitude of the heat of combustion of octane at constant volume is ____ kJmol−1kJ{mol}^{- 1} (nearest integer).

  9. Question 9

    This type asked 4 times: 28 Jun 2022, 30 Jan 2023, 1 Feb 2024, 2 Apr 2025. This one: 2 Apr 2025 See all 4 of this type

    31
    Two vessels A and B are connected via stopcock. The vessel A is filled with a gas at a certain pressure. The entire assembly is immersed in water and is allowed to come to thermal equilibrium with water. After opening the stopcock the gas from vessel A expands into vessel BB and no change in temperature is observed in the thermometer. Which of the following statement is true?

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  10. Question 10

    Asked 3 times: 2021 Paper 19*, 26 Jun 2022*, 8 Apr 2024 (* = numbers or wording changed that year) See all 3 times it was asked

    141
    Δvap H⊖\Delta_{\text{vap~}}H^{\ominus} for water is +40.49 kJ mol−1+ 40.49\text{ }kJ{\text{ }mol}^{- 1} at 1 bar and 100∘C100^{\circ}C. Change in internal energy for this vapourisation under same condition is _______ JJ mol−1mol^{- 1}. (Integer answer) (Given R=8.3JK−1 mol−1R = 8.3JK^{- 1}{\text{ }mol}^{- 1} )