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Thermodynamics · Question 3

JEE Main 2026 (Online) 6th April Morning ShiftNumericalMedium📈 Topic in 23% papers+4
1

Consider the reaction X Y at 300 K. If H and K are 28.40 kJ mol-1 and 1.8 10-7 at the same temperature, then the magnitude of S for the reaction in J K-1 mol-1 is . (Nearest integer) (Given : R = 8.3 J K-1 mol-1, ln 10 = 2.3, log 3 = 0.48, log 2 = 0.30)

Answer

34

Solution

G = -2.303RT K

log K = log(1.8 × 10-7) = log 18 − 7 − 1 = log 18 − 8

log 18 = log 2 + 2 log 3 = 0.30 + 0.96 = 1.26 ⇒ log K = −6.74

⇒ G = -2.3 8.3 300 (-6.74)

⇒ G = +38600 J mol-1

G = H - T S

⇒ S = H - G T

⇒ S = 28400 - 38600300

⇒ S = −34 J K-1 mol-1

∴ Magnitude of S = 34

Answer: 34

JEE Main 2026 (Online) 6th April Morning Shift

Keep practising — Thermodynamics

2

Match List - I with List - II. Given V1 and V2 are initial and final volumes respectively. Choose the correct answer from the options given below :

  1. A-II, B-III, C-I, D-IV
  2. A-II, B-I, C-IV, D-III
  3. A-II, B-I, C-III, D-IV
  4. A-I, B-II, C-III, D-IV
JEE Main 2026 (Online) 6th April Evening Shift
3

Consider the following data for the reaction X2(g) + Y2(g) 2XY(g) at 600 K. The rG (in kJ mol-1) for the reaction is : array|c|c|c| Compound & fH 600 K ( kJ mol-1) & S 600 K ( J mol-1 K-1) \ XY(g) & 42 & 200 \ X2(g) & 8 & 140 \ Y2(g) & 80 & 250 \ array

  1. −21000
  2. −10
  3. −1000
  4. −9.012
JEE Main 2026 (Online) 5th April Evening Shift
4

The correct order of molar heat capacities measured at 298 K and 1 bar is :

  1. Copper(s) > Bromine(l) > Helium(g)
  2. Bromine(l) > Copper(s) > Helium(g)
  3. Helium(g) > Bromine(l) > Copper(s)
  4. Helium(g) > Bromine(l) = Copper(s)
JEE Main 2026 (Online) 5th April Evening Shift
5

Given below are two statements : In the light of the above statements, choose the correct answer from the options given below

  1. Both Statement I and Statement II are true
  2. Both Statement I and Statement II are false
  3. Statement I is true but Statement II is false
  4. Statement I is false but Statement II is true
JEE Main 2026 (Online) 4th April Morning Shift
6

If 3.365 g of ethanol (l) is burnt completely in a bomb calorimeter at 298.15 K, the heat produced is 99.472 kJ. The | Hf | of ethanol at 298.15 K is 102 kJ mol-1. (Nearest integer) Given: Standard enthalpy for combustion of graphite = −393.5 kJ mol-1 Standard enthalpy of formation of water (l) = −285.8 kJ mol-1 Molar mass in g mol-1 of C, H, O are 12, 1 and 16 respectively

JEE Main 2026 (Online) 4th April Evening Shift
7

Consider the following data. (i) 2Al(s) + 6HCl(aq) Al2Cl6(aq) + 3H2(g) + 1200 kJ/mol (ii) H2(g) + Cl2(g) 2HCl(g) + 164 kJ/mol (iii) HCl(g) + aq HCl(aq) + 83 kJ/mol (iv) Al2Cl6(s) + aq Al2Cl6(aq) + 663 kJ/mol The enthalpy of formation of anhydrous solid Al2Cl6 is :

  1. -648 kJ mol-1
  2. -1350 kJ mol-1
  3. -2002 kJ mol-1
  4. -1527 kJ mol-1
JEE Main 2026 (Online) 2nd April Morning Shift
8

At the transition temperature T, A B and G = 105 - 35 T where A and B are two states of substance X. The transition temperature in °C when pressure is 1 atm is . (Nearest integer)

JEE Main 2026 (Online) 2nd April Morning Shift
9

Gas 'A' undergoes change from state 'X' to state 'Y'. In this process, the heat absorbed and work done by the gas is 10 J and 18 J respectively. Now gas is brought back to state 'X' by another process during which 6 J of heat is evolved. In the reverse process of 'Y' to 'X',

  1. 18 J of the work is done by the gas 'A'.
  2. 2 J of the work is done by the gas 'A'.
  3. 12 J of the work is done on the gas 'A' by the surrounding.
  4. 14 J of the work is done on the gas 'A' by the surrounding.
JEE Main 2026 (Online) 2nd April Evening Shift
10

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
JEE Main 2026 (Online) 28th January Morning Shift
11

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

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