JEE MAIN - Chemistry (2010 - No. 26)
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 x 108 ms–1 and NA = 6.02 x 1023 mol–1)
(c = 3 x 108 ms–1 and NA = 6.02 x 1023 mol–1)
594 nm
640 nm
700 nm
494 nm
Explanation
Energy required to break one Cl2 molecule = $${{242 \times {{10}^3}} \over {6.02 \times {{10}^{23}}}}$$ J
As E = $${{hc} \over \lambda }$$
So $$\lambda = {{hc} \over E}$$
= $${{6.626 \times {{10}^{ - 34}} \times 3 \times {{10}^8} \times 6.02 \times {{10}^{23}}} \over {242 \times {{10}^3}}}$$
= 494 $$ \times $$ 10-9 m
= 494 nm
As E = $${{hc} \over \lambda }$$
So $$\lambda = {{hc} \over E}$$
= $${{6.626 \times {{10}^{ - 34}} \times 3 \times {{10}^8} \times 6.02 \times {{10}^{23}}} \over {242 \times {{10}^3}}}$$
= 494 $$ \times $$ 10-9 m
= 494 nm
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