The amount of UVA radiation hitting a surface at sea level in a lightly clouded day is about 70W/m2. About half of that can be absorbed by the skin. A typical carbon- carbon bond requires 348 kJ/mol to break. A person lies on the beach for about 1 hour without sunscreen (i. e. fully exposed to UVA radiation). Estimate the number of C-C bonds broken in this person’s back (about 0.18 m2) over that period. Assume that the average wavelength of UVA is 335 nm.

Explanation:

Area of person's back = .18 m²

energy of radiation falling on the back per second

= 70 x .18 J

= 12.6J

Energy absorbed per second = .5 x 12.6 = 6.3 J

energy absorbed per hour = 6.3 x 60 x 60 = 22680 J

energy required to break one mole bond = 348 x 10³ J  

energy required to break one bond = 348 x 10³ / 6.02 x 10²³

= 57.8 x 10⁻²⁰ J .

So number of bonds broken in one hour = 22680 / 57.8 x 10⁻²⁰

= .392  x 10²³ bonds .

= 39.2 x 10²⁰ bonds .

a corroding iron, if that's one of your choices