Book contents
- Frontmatter
- Contents
- Preface to first edition
- Preface to second edition
- 1 Chemical equilibrium
- 2 Chemical thermodynamics
- 3 Chemical kinetics
- 4 Solution chemistry and aqueous equilibria
- 5 Acids and bases
- 6 Oxidation–reduction reactions
- 7 Photochemistry
- Appendix I International system of units (SI)
- Appendix II Some useful numerical values
- Appendix III Atomic weights
- Appendix IV Equilibrium (or dissociation) constants for some chemical reactions
- Appendix V Some molar standard Gibbs free energies of formation, molar standard enthalpies (or heats) of formation, and molar absolute entropies at 25°C and 1 atmosphere
- Appendix VI Names, formulas, and charges of some common ions
- Appendix VII Answers to exercises and hints and solutions to selected exercises
- Index
7 - Photochemistry
Published online by Cambridge University Press: 05 June 2012
- Frontmatter
- Contents
- Preface to first edition
- Preface to second edition
- 1 Chemical equilibrium
- 2 Chemical thermodynamics
- 3 Chemical kinetics
- 4 Solution chemistry and aqueous equilibria
- 5 Acids and bases
- 6 Oxidation–reduction reactions
- 7 Photochemistry
- Appendix I International system of units (SI)
- Appendix II Some useful numerical values
- Appendix III Atomic weights
- Appendix IV Equilibrium (or dissociation) constants for some chemical reactions
- Appendix V Some molar standard Gibbs free energies of formation, molar standard enthalpies (or heats) of formation, and molar absolute entropies at 25°C and 1 atmosphere
- Appendix VI Names, formulas, and charges of some common ions
- Appendix VII Answers to exercises and hints and solutions to selected exercises
- Index
Summary
A molecule may absorb electromagnetic (em) radiation and, in the process, break down into its atomic or molecular components. Unstable atoms and molecular fragments may also combine to form more stable molecules, disposing of their excess energy in the form of em radiation. These chemical reactions are called photochemical, and the process by which a photochemical reaction occurs is called photolysis. Photochemical reactions play very important roles in many aspects of environmental chemistry. Therefore, this book concludes with a brief account of some of the basic principles of photochemistry, which we will then apply to ozone in the Earth's stratosphere and the problem of the stratospheric ozone hole.
Some properties of electromagnetic waves
Electromagnetic radiation has both wave and particle characteristics. Considered as a wave, em radiation may be viewed as an ensemble of waves that travels through a vacuum with the speed of light, c = 2.998 x 108ms-1. The distance between two successive crests in the intensity of the radiation is called the wavelength (λ) of the radiation. The frequency (v) of the radiation is the number of crests in intensity that pass a given point in one second. The units of v are s-1 or hertz (Hz). If v crests in intensity pass a given point in one second, one crest passes a given point in 1/v seconds. Therefore, a crest in intensity of an em wave travels a distance λ in 1/v seconds.
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- Basic Physical Chemistry for the Atmospheric Sciences , pp. 137 - 158Publisher: Cambridge University PressPrint publication year: 2000