Calculate the energy for one mole of photons (an einstein) for light absorbed at 6.90 * 102 nm.

We know that:

f * λ = c

and

E = h*f

so, rearranging:

E/h = C/λ

given:

h = 6.90 * 10^2 nm

substituting the values:

E = C/λ x h

(c is the speed of light; that is 3x10^8 m/s)

= 3x10^8 x 6.626x10^-34 / 6.90 x10^7m x 6.022x10^23

Hence,

using calculator:

we get,

E = 1.69 x 10^5 Joules