Chapter 9: Reaction Systems
- Page ID
- 354129
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In the real world, simple chemical reaction systems are rare. Chemistry lab experiments typically involve mixing pure chemicals together in well-defined amounts under tightly-controlled conditions. In the wild, things are messier. There are usually a number of chemical species present, and this leads to competing reactions. Laboratory systems are effectively closed systems, and the results are analyzed only after the reaction has reached equilibrium. Real systems, on the other hand, are usually open and rarely reach equilibrium. This is particularly true for living systems, which tend to die if they reach equilibrium or become enclosed. In fact, most real systems are subject to frequent short- and long-term perturbations. We learned in the last chapter that perturbations (adding or taking away a product or a reactant) lead to compensatory changes and the system responds, as described by Le Chatelier’s principle. In the context of a more complex system, this simple behavior can produce quite dramatic results. Life is an example of such a system that has survived in its various forms uninterrupted for over \(3.5\times 10^{9}\) years.
In this chapter, we examine a range of complex systems and consider how living systems keep the concentration of important chemical species at a reasonable level (for example, by buffering the \(\mathrm{pH}\)); how they use differences in concentrations of chemical species to drive cellular processes (like thought); and how reactions that release energy (by forming more stable compounds with stronger bonds) can be coupled to reactions that require energy in order to occur.