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JEE Main Chemistry Thermodynamics (C) 2026 JEE Main 2026 (22 January Shift 2)

JEE Main Chemistry Question (2026) — Solution

Question

If the enthalpy of sublimation of Li is 155 ~kJ ~mol ^ -1 , enthalpy of dissociation of F _ 2 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)

Options

  1. A. A
  2. B. B
  3. C. C
  4. D. D

Answer

A. A

Step-by-step solution

Using Born-Haber cycle: H_f(LiF) = H_ sub (Li) + 1 2 H_ diss (F_2) + H_ ie (Li) + H_ eg (F) - U_ lattice Substituting values: -594 = 155 + 1 2 (150) + 520 + (-313) - U_ lattice -594 = 155 + 75 + 520 - 313 - U_ lattice -594 = 437 - U_ lattice U_ lattice = 437 + 594 = 1031 kJ/mol

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