Question

 The energy required to break one mole of Cl–Cl bonds in Cl₂ is 242 kJ mol^-1. The longest wavelength of light capable of breaking a single Cl–Cl bond is

(C = 3×10⁸ m/s and N_A = 6.02×10²³ mol^-1)

(1) 494 nm

(2) 594 nm

(3) 640 nm

(4) 700 nm

Answer 1

(1) 494 nm 

We have B.E = 242KJ/Mol

E = h_cN_A/λ

∴ λ = h_cN_A/E

= 3×10⁸×6.626×10^-34×6.02×10²³/(242×10³)

= 0.494×10^-3×10³

= 494 nm