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:

energy of solar radiation = 70 W / m²

energy absorbed in 1 hour by an area of .18 m²

= 70 x .5 x .18 x 60 x 60 J

= 22.68 x 10³ J

bond energy of i mole bond = 348 x 10³ J

bond energy of 6.02 x 10²³ bonds = 348 x 10³  J

bond energy of one bond = 57.8 x 10⁻²⁰ J  

No of bonds broken by energy 22.68 x 10³

= 22.68 x 10³  / 57.8 x 10⁻²⁰

= .3923 x 10²³

= 39.23 x 10²⁰ .

- "the choice that is not an indicator of a chemical change is "state of matter changes". more common than not, chemical reactions produce energy in the form of light or heat. along with energy, they also produce a new substance called the product that could be in any state of matter (solid, gas, or liquid)."