In secondary-school chemistry, reaction rate and equilibrium are core topics. Ostwald plotted experimental data to show systematically how reaction speed changes with temperature and concentration. The rate laws he established still appear in textbooks as the basic equations connecting concentration and time. As a reaction proceeds, the ratio of products to reactants reaches a constant value called chemical equilibrium. Ostwald stressed that this state is a dynamic equilibrium, with molecules reacting in both directions. He also proved that catalysts accelerate reactions by lowering the activation energy and offering an alternate pathway. Industry exploits this knowledge to optimize ammonia synthesis, petroleum refining, and more, saving resources and energy. His work therefore underpins both theory and practical technology that sustain modern society.

Ostwald is regarded as one of the founders of physical chemistry, deriving quantitative kinetics and equilibrium theory from experimental data. In his 1884 paper he proposed the differential rate law v = k[A]^n containing the rate constant k and reaction order n, and illustrated how to extract k from integrated concentration–time curves. The methodology has since been applied to systems ranging from radical polymerizations to enzyme catalysis. Regarding equilibrium, he related his measurements to Gibbs free energy, experimentally validating the condition ΔG = 0 at equilibrium. He formalised the catalytic lowering of activation energy and clarified that catalysts alter rate but not equilibrium position. By advancing the acid–base concept he introduced the Ostwald dilution law K_d = α^2/(1-α)·C, enabling quantitative evaluation of weak electrolytes. These achievements provided experimental support for van ’t Hoff’s law of mass action, bridging thermodynamics and kinetics. He proposed the partition principle, influencing liquid–liquid extraction techniques based on hydrophilic/hydrophobic distribution. His results were compiled in “Lehrbuch der Allgemeinen Chemie,” a cornerstone for chemical education and research. Modern catalyst chemistry, reaction engineering and environmental chemistry owe much to his foundational work.

By verifying the law of mass action, Ostwald linked the temperature dependence of the rate constant k to Arrhenius’ exponential form, systematising the activation-energy concept. His dilution law preceded Debye–Hückel theory and became the standard route to evaluate equilibrium constants of weak electrolytes. In catalysis he qualitatively estimated transition-state energy profiles for heterogeneous and homogeneous systems and articulated “Ostwald’s Principle,” that catalysts alter rate but not equilibrium distribution. Spectral data combined with partition coefficients led to molecular identification schemes that later matured into chromatography theory. As head of the Leipzig school he co-founded the Bunsen society with Nernst and Arrhenius, promoting data sharing and interdisciplinary collaboration. In his Lehrbuch he derived integrated first- and second-order expressions and outlined multi-step mechanism analysis including pseudo-first-order and steady-state approximations. He redefined chemical affinity as the gradient of Gibbs energy, providing a mathematical description of the driving force in non-equilibrium processes. These contributions cemented the fusion of kinetics and thermodynamics in the early 20th century and underpin modern catalyst design.