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18 Chemistry of the Environment Solutions to Exercises (a) Ultraviolet (Figure 6.4) (b) = = 6.626 10⁻³⁴ J 3.00 10⁸ m/s = 5.934 X 10⁻¹⁹ 335 10⁻⁹ m = 5.93 J/photon 5.934 1 photon 10⁻¹⁹ J 6.022 1 mol photons = 357 kJ/mol (c) The average C-H bond energy from Table 8.4 is 413 kJ/mol. The energy calculated in part (b), 357 kJ/mol, is the energy required to break 1 mol of C-H bonds in formaldehyde, The C-H bond energy in must be less than the "average" C-H bond energy. :O: :O: (d) H-C-H + + H 18.32 (a) Visible (Figure 6.4) (b) = = 6.626 10⁻³⁴ 420 10⁻⁹ X 3.00 m 10⁸ m/s = 4.733 10⁻¹⁹ = 4.73 4.733 1 photon X 10⁻¹⁹ J 6.022 1 10²³ mol photons = 285 kJ/mol (c) + hv 18.33 Most of the energy entering the atmosphere from the sun is in the form of visible radiation, while most of the energy leaving the earth is in the form of infrared radiation. is transparent to the incoming visible radiation, but absorbs the outgoing infrared radiation. 18.34 (a) A greenhouse gas absorbs energy in the 10,000-30,000 nm or infrared region. It absorbs wavelengths of radiation emitted by earth and returns it as heat. A non- greenhouse gas is transparent to radiation in this wavelength range. (b) CH₄ (g) contains 4 C-H bonds, while N₂ has one strong triple bond. Infrared ra- diation has insufficient energy to cause electron transitions or bond cleavage; but it has an appropriate amount of energy to cause molecular deformations, bond stretching, and angle bending. The CH₄ molecule absorbs infrared radiation while undergoing these deformations, but symmetrical diatomic gases such as N₂ cannot "use" infrared radiation and are transparent to it. Earth's Water (section 18.3) 18.35 Analyze/Plan. Given salinity and density, calculate molarity. A salinity of 5.6 denotes that there are 5.6 g of dry salt per kg of water. Solve. 5.6 g NaCl 1.03 kg soln 1 mol NaCl 1 mol = 0.0987 = 0.099 M 1 kg soln 1L soln 58.44 g NaCl 1 mol NaCl 18.36 If the phosphorous is present as phosphate, there is a 1:1 ratio between the molarity of phosphorus and molarity of phosphate. Thus, we can calculate the molarity based on the given mass of P. 557