Thermodynamics

Thermodynamics

Question

The energy required to break one mole of Cl— Cl bonds in Cl2 is 242 kJ mol. The longest wavelength of light capable of breaking a single Cl — Cl bond is
(c= 3 x 108 ms–1and NA = 6.02 x 1023 mol–1)

  • 594 nm

  • 640 nm

  • 700 nm

  • 494

Answer

D.

494

Energy, E = NA
hv space equals space straight N subscript straight A space straight x space hc over straight lambda
or space straight lambda space equals space straight N subscript straight A space straight x space hc over straight E
straight lambda space equals space fraction numerator 6.626 space straight x space 10 to the power of negative 34 end exponent space straight x space 3 space straight x space 10 to the power of 8 space straight x space 6.02 space space straight x space 10 to the power of 23 over denominator 242 space straight x space 10 cubed end fraction
space 494 space straight x space 10 to the power of negative 9 end exponent space straight m equals space 494 space nm

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