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Thermodynamics · Question 12

JEE Main 2026 (Online) 28th January Morning ShiftMCQEasy📈 Topic in 32% papers+4−1
1

20.0 dm3 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: 2 = 0.3010 and 5 = 0.6989)

  1. w = -9.1 kJ, U = 0, H = 0, q = 9.1 kJ
  2. w = 9.1 J, U = 9.1 J, H = 0; q = 0
  3. w = -3.9 kJ, U = 0, H = 0; q = 3.9 kJ
  4. w = +4.1 kJ, U = 0, H = 0; q = -4.1 kJ

Answer

(1) w = -9.1 kJ, U = 0, H = 0, q = 9.1 kJ

Solution

For an ideal gas at constant temperature, U = 0 and H = 0.

Work in isothermal reversible expansion:

w = -2.303 nRT P1P2, and nRT = P1V1

P1V1 = (0.5 106 Pa)(20.0 10-3 m3) = 1.0 104 J

0.50.2 = 2.5 = 5 - 2 = 0.6989 - 0.3010 = 0.3979

w = -2.303 1.0 104 0.3979 J

w = -9.16 103 J -9.1 kJ

First law: U = q + w = 0

q = -w = +9.1 kJ

Answer: (1)

JEE Main 2026 (Online) 28th January Morning Shift

Keep practising — Thermodynamics

2

The plot of 10 K vs 1T gives a straight line. The intercept and slope respectively are (where K is the equilibrium constant).

  1. - S R2.303, H R2.303
  2. - H 2.303R, S 2.303R
  3. S 2.303R, - H 2.303R
  4. 2.303R H , 2.303R S
JEE Main 2026 (Online) 28th January Evening Shift
3

Match the LIST-I with LIST-II Choose the correct answer from the options given below:

  1. A-IV, B-I, C-III, D-II
  2. A-I, B-III, C-II, D-IV
  3. A-II, B-I, C-III, D-IV
  4. A-IV, B-II, C-III, D-I
JEE Main 2026 (Online) 24th January Morning Shift
4

The heats of atomisation of methane and ethane are 'x' kJ mol-1 and 'y' kJ mol-1 respectively. The longest wavelength ( ) of light capable of breaking the C-C bond can be expressed in SI unit as :

  1. NA hc250(y - 6x)
  2. NA hc (y - 6x4 )-1
  3. hc1000 ( y - 6x4 )-1
  4. NA hc250(4y - 6x)
JEE Main 2026 (Online) 24th January Evening Shift
5

A cup of water at 5 C (system) is placed in a microwave oven and the oven is turned on for one minute during which the water begins to boil. Which of the following options is true?

  1. q = +ve, w = -ve, U = +ve
  2. q = +ve, w = 0, U = -ve
  3. q = +ve, w = -ve, U = -ve
  4. q = -ve, w = -ve, U = -ve
JEE Main 2026 (Online) 23rd January Morning Shift
6

Match the LIST-I with LIST-II Choose the correct answer from the options given below :

  1. A-I, B-II, C-III, D-IV
  2. A-III, B-II, C-IV, D-I
  3. A-II, B-I, C-III, D-IV
  4. A-II, B-III, C-I, D-IV
JEE Main 2026 (Online) 22nd January Morning Shift
7

If the enthalpy of sublimation of Li is 155 kJ mol-1, enthalpy of dissociation of F2 is 150 kJ mol-1, ionization enthalpy of Li is 520 kJ mol-1, electron gain enthalpy of F is -313 kJ mol-1, standard enthalpy of formation of LiF is -594 kJ mol-1. The magnitude of lattice enthalpy of LiF is kJ mol-1. (Nearest Integer)

JEE Main 2026 (Online) 22nd January Evening Shift
8

Which of the following graphs between pressure 'p' versus volume 'V' represents the maximum work done?

  1. [figure]
  2. [figure]
  3. [figure]
  4. [figure]
JEE Main 2026 (Online) 21st January Morning Shift
9

Use the following data : array|c|c|c| Substance & f H (500 K) kJ mol-1 & S (500 K) J K-1 mol-1 \ AB(g) & 32 & 222 \ A2(g) & 6 & 146 \ B2(g) & x & 280 \ array One mole each of A2(g) and B2(g) are taken in a 1 L closed flask and allowed to establish the equilibrium at 500 K. A2(g) + B2(g) 2AB(g) The value of x (in kJ mol-1) is . (Nearest integer) (Given : K = 2.2, R = 8.3 J K-1 mol-1)

JEE Main 2026 (Online) 21st January Morning Shift
10

Consider the following data : f H (methane, g) = -X kJ mol-1 Enthalpy of sublimation of graphite = Y kJ mol-1 Dissociation enthalpy of H2 = Z kJ mol-1 The bond enthalpy of C–H bond is given by :

  1. X+Y+2Z4
  2. X+Y+4Z2
  3. -X+Y+Z4
  4. X+Y+Z
JEE Main 2026 (Online) 21st January Evening Shift
11

Resonance in X2Y can be represented as [figure] The enthalpy of formation of X2Y ( X X(g) + 12Y = Y(g) X2Y(g) ) is 80 kJ mol-1. The magnitude of resonance energy of X2Y is kJ mol-1 (nearest integer value). Given: Bond energies of X X, X = X, Y = Y and X = Y are 940, 410, 500, and 602 kJ mol-1 respectively. Valence X: 3, Y: 2

JEE Main 2025 (Online) 8th April Evening Shift

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