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Question: The energy required to break one mole of Cl – Cl bonds in Cl2 is 242 kJ mol–1 . The longest waveleng...

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–1 and NA = 6.02 × 1023mol–1)

A

594 nm

B

640 nm

C

700 nm

D

494 nm

Answer

494 nm

Explanation

Solution

Cl–Cl(g) ⟶\longrightarrow 2Cl(g) ;Δ\DeltaH = 242 KJ mol

= 242×1036.02×1023\frac{242 \times 10^{3}}{6.02 \times 10^{23}} J molecule–1

E =hcλ\frac{hc}{\lambda}

242×10−23×1036.02=6.6×10−34×3×108λ\frac{242 \times 10^{- 23} \times 10^{3}}{6.02} = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{\lambda}

λ=6.6×10−34×3×108242×10−23×103=6.6×3×6.02242×10−5\lambda = \frac{6.6 \times 10^{- 34} \times 3 \times 10^{8}}{242 \times 10^{- 23} \times 10^{3}} = \frac{6.6 \times 3 \times 6.02}{242} \times 10^{- 5}

= 0.494 ´ 10–6

= 494 ´ 10–9 m = 494 nm