Physical chemistry
= Physical chemistry
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<Physical chemistry> explains chemical behavior using quantitative relations between molecular structure, energy, motion, and matter. <Chemical thermodynamics> describes equilibrium and energy constraints, <chemical kinetics> describes reaction rates, and quantum and statistical descriptions connect those observations to microscopic states.
For example, thermodynamics can predict an equilibrium product ratio without predicting how quickly it is reached. A catalyst can accelerate the approach while leaving that equilibrium unchanged. Spectroscopy then supplies a separate test of molecular energy levels and structure. Combining these measurements helps distinguish a plausible mechanism from one that fits only a single observation.