Module 3 Conceptual Integration
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Chemical change
Each physics and chemistry topic we've covered so far has its domain. There are traditional problems - the time of a projectile in flight, the block sliding down an inclined plane, building up an atom, predicting a molecule's geometry, and so on. You will do your share of straightforward practice in MCAT review. There will be some questions like this on the exam, that could have been lifted from a 101 course, but, actually, not that many. You are responsible for the learning goals within each topic, but there are bigger learning goals we are working towards. We do all these practice items to build a tacit knowledge of how physical and chemical systems behave. An overarching goal throughout these early modules is to build our conceptual foundation for biochemistry.
In earlier modules, we have worked to understand the mechanics and electrodynamics of systems of charged particles. We applied this to help our understanding of the structure of matter at the atomic, molecular, and intermolecular levels. In this third module, we begin to analyze chemical transformations from the point of view of a system comprised of a huge number of molecules, the point of view of thermodynamics. What happens at the particle level translates in statistical aggregate as a change in a state function of the entire system, the internal energy change, ΔU.
If the internal energy of a system is changing, or if there is presssure-volume work being performed, we can apply the principle of conservation of energy, the 1st law of thermodynamics, to understand the heat flow between the system and its surroundings. We'll define a state function whose change, under constant pressure, is equal to the heat flow, the enthalpy change, ΔH. Understanding enthalpy change is a main goal in module 3.
In the future, next week maybe, we'll start module 4, and will see how the heat flow helps us understand why a chemical reaction may or may not be spontaneous. That's where we're heading - the free energy change, ΔG. To understand chemical change clearly is to move from the internal energy change, ΔU, then through the first law to heat flow, ΔH, then through the second law to free energy change, ΔG. There's a reason AAMC mentions free energy change more often than any other science concept in their topic outline. When you build up chemical thermodynamics from its foundations so that it becomes a form of tacit knowledge, you are able to see the plot in energy metabolism. Learning biochemistry stops being about memorization and becomes about understanding. This is one of the most important figures of merit for the MCAT. AAMC has a million ways to see if you have crossed this bridge.