Integrated SequencePhysics Chemistry Organic Biology

Web Resources

Chem1 Virtual Textbook - The direction of spontaneous change
Outstanding overview of the conceptual heart of Chemical Thermodynamics.

Chem1 Virtual Textbook - Chemical Energetics
Truly excellent survey of Thermochemistry. Before going deeper into Chemical Thermodynamics and Equilibrium, first make sure you understand Internal Energy change and Enthalpy change, the heart of Thermochemistry. A good understanding of Thermochemistry and Chemical Thermodynamics will make Biochemistry much easier and much more interesting.

Purdue University - Gas-Phase Reactions
This discussion of gas-phase reactions provides a very good pathway to understanding how reactions progress towards the equilibrium state.



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Special points of emphasis

Abnormal Psychology

Chemical Thermodynamics and the Equilibrium State

In our earlier discussion of Thermochemistry, we reviewed the concepts of internal energy change and enthalpy change. This equipped us to describe the changes in a substance as a thermochemical system. We learned how to compare the products and reagents in a chemical reaction in terms of the allotment of energy between the system and its surroundings. If the system completely changed from Reagents A to Products B, does heat flow in or out? At this stage, we are ready to seek to understand spontaneity in chemical transformations. What is the availability of energy in a chemical system for drive a reaction forward? We are describing the free energy in a chemical system, energy that when it is expended during chemical tranformation increases the entropy of the universe. Free energy is expended until the equilibrium state for the system is achieved. At equilibrium, heat flows between the system and its surroundings become microscopically reversible. The forward direction is just as likely as the reverse because the entropy associated with heat flows in either direction is the same.

On the MCAT, although you probably will run into a Le Châtelier's Principle question or two, the importance of this topic is very great besides direct questions on the MCAT because the concepts discussed here are the scaffolding on which much else is built. Most students find chemical thermodynamics to be a very abstract subject. I think this unfortunate situation occurs because of the way that chemical thermodynamics is approached in undergraduate general chemistry, without physics to make it intuitive and biology to make it concrete. If you approach chemical thermodynamics, though, with a basis in force and energy, you can relate the internal energy changes driving heat flow and entropy change to a fundamental understanding of the particle level of substances. Furthermore, when you bring chemical thermodynamics to your understanding of biochemistry, your appreciation of life processes will become much more coherent and much more interesting. This is the kind of intuitive feel for science that the MCAT writers are ultimately looking for with their exam.








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