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Thermodynamics · Question 34

JEE Main 2025 (Online) 2nd April Morning ShiftMCQEasy📈 Topic in 32% papers+4−1
1

[figure] 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 B and no change in temperature is observed in the thermometer. Which of the following statement is true ?

  1. dq 0
  2. The pressure in the vessel B before opening the stopcock is zero
  3. dw 0
  4. dU 0

Answer

(2) The pressure in the vessel B before opening the stopcock is zero

Solution

This is Joule's experiment on free expansion of a gas into an evacuated vessel.

Vessel B is evacuated the pressure in B before opening the stopcock is zero.

Gas expands against zero external pressure w = -pext V = 0, so dw = 0.

No change in temperature of the water no heat exchanged dq = 0.

By the first law, dU = dq + dw = 0.

Only statement (2) is true.

Answer: (2)

JEE Main 2025 (Online) 2nd April Morning Shift

Keep practising — Thermodynamics

2

Arrange the following in order of magnitude of work done by the system/on the system at constant temperature. (a) | wreversible| for expansion in infinite stages. (b) | wirreversible| for expansion in single stage. (c) | wreversible| for compression in infinite stages. (d) | wirreversible| for compression in single stage. Choose the correct answer from the options given below:

  1. d > c = a > b
  2. c = a > d > b
  3. a > c > b > d
  4. a > b > c > d
JEE Main 2025 (Online) 2nd April Evening Shift
3

Which of the following graphs correctly represents the variation of thermodynamic properties of Haber's process?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2025 (Online) 2nd April Evening Shift
4

500 J of energy is transferred as heat to 0.5 mol of Argon gas at 298 K and 1.00 atm. The final temperature and the change in internal energy respectively are: Given: R = 8.3 J K-1 mol-1

  1. 368 K and 500 J
  2. 348 K and 300 J
  3. 378 K and 300 J
  4. 378 K and 500 J
JEE Main 2025 (Online) 29th January Morning Shift
5

The formation enthalpies, Hf for H(g) and O(g) are 220.0 and 250.0 kJ mol-1, respectively, at 298.15 K, and Hf for H2O(g) is -242.0 kJ mol-1 at the same temperature. The average bond enthalpy of the O-H bond in water at 298.15 K is kJ mol-1 (nearest integer).

JEE Main 2025 (Online) 28th January Morning Shift
6

[figure] An ideal gas undergoes a cyclic transformation starting from the point A and coming back to the same point by tracing the path A→B→C→D→A as shown in the three cases above. Choose the correct option regarding U :

  1. U(Case-III) > U(Case-II) > U(Case-I)
  2. U(Case-I) > U(Case-II) > U(Case-III)
  3. U(Case-I) = U(Case-II) = U(Case-III)
  4. U(Case-I) > U(Case-III) > U(Case-II)
JEE Main 2025 (Online) 28th January Evening Shift
7

Consider the following data: Heat of formation of CO2(g) = -393.5 kJ mol-1 Heat of formation of H2O(l) = -286.0 kJ mol-1 Heat of combustion of benzene = -3267.0 kJ mol-1 The heat of formation of benzene is kJ mol-1. (Nearest integer)

JEE Main 2025 (Online) 28th January Evening Shift

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