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Thermodynamics

JEE Main 2025 (Online) 23rd January Morning ShiftMCQMedium📈 Topic in 3% papers+4−1
Ques. 1JEE Main 2025, 23 January (Morning Shift)

Ice at -5 C is heated to become vapor with temperature of 110 C at atmospheric pressure. The entropy change associated with this process can be obtained from

  1. 268 K273 K Cp,m dT + Hm, fusionTf + Hm, vaporisationTb + 273 K373 K Cp,m dT + 373 K383 K Cp,m dT
  2. 268 K383 K Cp dT + Hmelting273 + Hboiling373
  3. 268 K383 K Cp dT + qrevT
  4. 268 K273 K Cp,mT dT + Hm, fusionTf + Hm, vaporisationTb + 273 K373 K Cp,m dTT + 373 K383 K Cp,m dTT

Answer

(4) 268 K273 K Cp,mT dT + Hm, fusionTf + Hm, vaporisationTb + 273 K373 K Cp,m dTT + 373 K383 K Cp,m dTT

Solution

Concept: S = Cp dTT on heating, S = HT at a phase change.

Path: ice 268→273 K, melting at Tf, water 273→373 K, vaporisation at Tb, steam 373→383 K.

∴ three heating terms + two phase-change terms ⇒ option (4)

Answer: (4)

Keep practising — Thermodynamics

Ques. 2JEE Main 2025, 23 January (Morning Shift)

The standard enthalpy and standard entropy of decomposition of N2O4 to NO2 are 55.0 kJ mol-1 and 175.0 J/K/mol respectively. The standard free energy change for this reaction at 25 in J mol-1 is (Nearest integer)

Ques. 3JEE Main 2025, 23 January (Evening Shift)

The effect of temperature on spontaneity of reactions are represented as : [figure] The incorrect combinations are :

  1. A and C only
  2. B and D only
  3. A and D only
  4. B and C only
Ques. 4JEE Main 2025, 23 January (Evening Shift)

The bond dissociation enthalpy of X2 H bond calculated from the given data is kJ mol-1. (Nearest integer) M+X-(s) M+(g)+X-(g) H lattice=800 kJ mol-1 M(s) M(g) H sub=100 kJ mol-1 M(g) M+(g)+e-(g) H i=500 kJ mol-1 X(g)+e-(g) X-(g) H eg=-300 kJ mol-1 M(s)+ 12X2(g) M+X-(s) H f=-400 kJ mol-1 [Given : M+X- is a pure ionic compound and X forms a diatomic molecule X2 in gaseous state]

Ques. 5JEE Main 2025, 22 January (Morning Shift)

A liquid when kept inside a thermally insulated closed vessel at 25 was mechanically stirred from outside. What will be the correct option for the following thermodynamic parameters ?

  1. U = 0, q < 0, w > 0
  2. U > 0, q = 0, w > 0
  3. U = 0, q = 0, w = 0
  4. U < 0, q = 0, w > 0
Ques. 6JEE Main 2025, 22 January (Evening Shift)

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

  1. A-I, B-II, C-IV, D-III
  2. A-II, B-III, C-I, D-IV
  3. A-II, B-I, C-IV, D-III
  4. A-II, B-I, C-III, D-IV
Ques. 7JEE Main 2025, 22 January (Evening Shift)

Consider the following cases of standard enthalpy of reaction ( Hr in kJ mol-1) C2H6(g)+ 72O2(g) 2CO2(g)+3H2O(l) H1 =-1550 C(graphite)+O2(g) CO2(g) H2 =-393.5 H2(g)+ 12O2(g) H2O(l) H3 =-286 The magnitude of H f C2H6(g) is kJ mol-1 (Nearest integer).

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