JEE Main 2026 — Thermodynamics (C) Question with Solution
JEE Main 2026 (24 January Shift 2)
Question
The heat of atomisation of methane and ethane are ' x ' and ' y ' respectively. The longest wavelength of light capable of breaking the bond can be expressed in SI unit as:
Choose an option
Show full solutionCorrect option: A
Correct answer
A
Step-by-step explanation
Heat of atomization: CH₄ has x kJ/mol (4 C-H bonds), C₂H₆ has y kJ/mol (1 C-C + 6 C-H bonds)
Let C-H bond energy = a, C-C bond energy = b
Then: x = 4a and y = b + 6a
Solving: a = x/4, so b = y - 6x/4 = (4y - 6x)/4 kJ/mol
Converting to J/mol: b = (4y - 6x) × 250 J/mol
Using and :
(in SI units)
Let C-H bond energy = a, C-C bond energy = b
Then: x = 4a and y = b + 6a
Solving: a = x/4, so b = y - 6x/4 = (4y - 6x)/4 kJ/mol
Converting to J/mol: b = (4y - 6x) × 250 J/mol
Using and :
(in SI units)
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This is a previous-year question from JEE Main 2026, covering the Thermodynamics (C) chapter of Chemistry. PrepSharp catalogues every PYQ from JEE Main with a verified answer key and step-by-step solution prepared by IIT alumni — so you can search by chapter, topic or year and revise efficiently.