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 .

lithosphere and asthenosphere

1. for the first question, we must find the mass of the anhydrous salt, mgso₄. the molar mass for mgso₄·7h₂o is 246.47 g/mol, while that of mgso₄ is 120.37 g/mol.7.834 g mgso₄·7h₂o * 1 mol mgso₄·7h₂o/246.47 g * 1 mol mgso₄/1 mol mgso₄·7h₂o * 20.37 g mgso₄/mol = 0.647 g mgso₄

2. mass of water = mass of sample - mass of anhydrous salemass of water = 7.834 - 0.647 = 7.19 gpercent water in hydrate = 7.19/7.834 * 100 = 91.74%