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Standard XII

Chemistry

1900's Physics and Wave

Photochromic ...

Question

Photochromic sunglasses, which darken when exposed to light, contain a small amount of colourless $A g C l (s)$ embedded in the glass. When irradiated with light, metallic silver atoms are produced and the glass darkens.
$A g C l (s) ⟶ A g (s) + C l$
Escape of chlorine atoms is prevented by the rigid structure of the glass and the reaction therefore, reverses as soon as the light is removed. If $310 k J / m o l$ of energy is required to make the reaction proceed, what wavelength of light is necessary?

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Solution

Energy per mole $=$ Energy of one Einstein
i.e., energy of one mole quanta
$= \frac{N h c}{λ}$
$∴ 310 \times 1000 = \frac{6.023 \times 10^{23} \times 6.626 \times 10^{- 34} \times 3 \times 10^{8}}{λ}$
$λ = 3.862 \times 10^{- 7} m = 3862 \times 10^{- 10} m = 3862 ˚ A$ .

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Energy per mole = Energy of one Einsteini.e., energy of one mole quanta =Nhcλ∴310×1000=6.023×1023×6.626×10−34×3×108λλ=3.862×10−7m=3862×10−10m=3862˚A.

Energy per mole $=$ Energy of one Einstein
i.e., energy of one mole quanta
$= \frac{N h c}{λ}$
$∴ 310 \times 1000 = \frac{6.023 \times 10^{23} \times 6.626 \times 10^{- 34} \times 3 \times 10^{8}}{λ}$
$λ = 3.862 \times 10^{- 7} m = 3862 \times 10^{- 10} m = 3862 ˚ A$ .