TAILIEUCHUNG - Abiotic Transformations in the Environment

Understand the role of solar photons as an energy source for chemical reactions in the environment. • Describe, in general, the dynamics of excited states in producing products and photo-sensitized reactants. • Understand the major abiotic chemical reaction pathways in the environment. | Abiotic Transformations in the Environment Principles of Environmental Toxicology Instructor Gregory Möller . University of Idaho Principles of Environmental Toxicology Learning Objectives Understand the role of solar photons as an energy source for chemical reactions in the environment. Describe in general the dynamics of excited states in producing products and photo-sensitized reactants. Understand the major abiotic chemical reaction pathways in the environment. 2 Principles of Environmental Toxicology Learning Objectives Describe electrophillic nucleophillic hydrolysis and redox reactions. Summarize the basic reactions associated with the formation of the hole in the ozone layer. Summarize the reactions associated with the formation of acid rock drainage. Principles of Environmental Toxicology Photochemical Reactions Endothermic environmental chemical reactions can get required energy of reaction from solar photons. UV-Vis energy is strong enough to break some chemical bonds. -Available in the solar spectrum. E x 105 X kJ Einstein E x 104 X kcal mole photons. 3 4 Principles of Environmental Toxicology Electromagnetic Spectrum Principles of Environmental Toxicology Electromagnetic Spectrum Wavelength jim X-Rays Near Mid IR Microwave 5 Principles of Environmental Toxicology Absorption Photon absorption is a quantum event and the specific energies required for excitation and reaction are characteristic of the molecule. - IR absorption corresponds to vibrational excitation of chemical bonds. UV absorption corresponds to electronic excitation usually lone pair n electrons or delocalized n electrons. - Heteroatom n n - Conjugation n n 7 Principles of Environmental Toxicology Photochemical Reactions Excited molecules can undergo unimolecular or bimolecular reactions. - Unimolecular dissociation bond breaking intersystem crossing. Direct photolysis CH4 hu X 140 nm CH2 H2 - Bimolecular chemical reaction energy transfer. Mercury sensitized Hg 1S0 hu 253 .

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