181x Filetype PPTX File size 1.33 MB Source: www.geo.cornell.edu
Plan of the Course • The Geochemical Toolbox o Thermodynamics o Kinetics o Aquatic systems o Trace elements & magmatic systems o Isotopes • Radiogenic • Stable • The Big Picture: Cosmochemistry o Formation of the elements o Formation of the Earth and the Solar System • Chemistry of the Earth Other Info Text: White: Geochemistry, Wiley-Blackwell, • Grading: 40% Problem ISBN 978-0-470-65668-6 Sets (6 to 8),20% Prelim, 40% Final Exam • http ://www.geo.cornell.ed u/geology/classes/geo 455/EAS455. html • Office: 4112 Snee • Office Hours: no formal office hours – drop by anytime. Thermodynamics • Thermodynamics is the study of energy & its transformations. o Chemical changes involve energy; by “following the energy”, we can predict the ‘equilibrium’ state of a system and therefore the outcome of reactions. • For example, we can predict the minerals that will crystallize from a cooling magma. • We can predict that as the concentration of atmospheric CO 2 increases, so does that of the ocean and the calcium carbonate shells of oysters and skeletons of corals will become more soluble. o (This at first seems counter-intuitive, and has to do with a decrease in ocean pH). • Thermodynamics uses a macroscopic approach. o We can use it without knowledge of atoms or molecules. o We will occasionally consider the microscopic viewpoint using statistical mechanics when our understanding can be enhanced by doing so. Thermodynamics and Kinetics • The equilibrium state of a system is independent of any previous state. So, for example, if we do a partial melting experiment with rock, it should not matter if we start with a solid and partially melt it or with a melt and partially crystallize it, or whether we partially dissolve calcium carbonate or partially precipitate it. • Kinetics is the study of rates and mechanisms of reaction. Kinetics concerns itself with the pathway to equilibrium; thermodynamics does not. Very often, equilibrium in the Earth is not achieved, or achieved only very slowly, which naturally limits the usefulness of thermodynamics. ‘The System’ Four Kinds of Systems • A thermodynamic system is the part of the universe we are considering. Everything else is referred to as the surroundings. o We are free to define the ‘system’ anyway we chose. However, how we define it may determine whether we can successfully apply thermodynamics.
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