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The bond dissociation energy for one mole of Cl–Cl bonds in Cl₂ is 242 kJ mol⁻¹. What is the maximum wavelength of radiation that can just rupture one Cl–Cl bond? (Take c = 3 × 10⁸ m s⁻¹ and Nₐ = 6.02 × 10²³ mol⁻¹.)

1. 594 nm
2. 640 nm
3. 700 nm
4. 494 nm

Correct answer: 494 nm

Solution

Per-bond energy = 242000/6.02e23 = 4.02e-19 J; lambda = (6.626e-34 x 3e8)/4.02e-19 = 4.94e-7 m = 494 nm. The stored 594 nm is wrong.

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