Chemical thermodynamics

Chemical thermodynamics applies energy, entropy, and equilibrium principles to chemical systems. It predicts how composition, temperature, pressure, and phase affect reactions and material stability.

Gibbs free energy: A thermodynamic potential that predicts equilibrium and the maximum non-expansion work available at constant temperature and pressure. Its change determines whether a reaction is thermodynamically favorable under constant-temperature, constant-pressure conditions.
First law of thermodynamics: The principle that energy is conserved, changing form or moving between a system and its surroundings. It constrains the heat and work exchanged during chemical changes.
Hess's law: The principle that a reaction's enthalpy change is independent of the pathway between its initial and final states. It allows reaction enthalpies to be assembled from measured reactions with known values.
Chemical kinetics: The study of reaction rates and the mechanisms by which chemical reactions occur. Thermodynamics predicts feasible equilibrium states, while kinetics determines how quickly they are reached.
Chemical potential: The change in a system's thermodynamic potential when the amount of a component changes, with other variables held fixed. Differences in chemical potential drive reactions, diffusion, and phase transfer.
Second law of thermodynamics: The principle that the total entropy of an isolated system cannot decrease in a spontaneous process. It supplies the entropy criterion from which chemical spontaneity and equilibrium conditions follow.
Calorimetry: The measurement of heat transferred during physical or chemical changes. Calorimetric data provide enthalpy changes used in thermodynamic calculations.
Statistical mechanics: A framework that derives macroscopic thermodynamic properties from the statistical behavior of microscopic states. It explains the molecular origins of thermodynamic quantities used in chemical predictions.
Chemical equilibrium: A state in which forward and reverse chemical reactions proceed at equal rates, leaving composition macroscopically constant. Equilibrium composition follows from minimizing Gibbs free energy at fixed temperature and pressure.
Enthalpy: A thermodynamic state function equal to internal energy plus pressure multiplied by volume. At constant pressure, its change equals heat transfer when only pressure-volume work occurs.

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