Complex chemical processes take place in physical plasmas, in which electrons with high average energy can also be involved. Physical plasmas are multiparticle systems in the form of fluid or gaseous mixtures of free electrons and ions as well as neutral particles and photons. The chemical conversions including the processes in the volume and at the plasma interfaces are summarized under the term plasma chemistry. Generally, a distinction is made between thermal and nonthermal plasmas. In thermal plasmas, a thermal equilibrium of all individual components with and between each other exists, and the law of mass action applies. In nonthermal plasmas, there is a thermodynamic nonequilibrium between electrons on the one hand and ions and neutral particles on the other. The average energy of the electrons can exceed that of the neutral particles and ions by up to three orders of magnitude, the latter of which can be close to room temperature. Plasma chemistry is still an interesting field of research today, and plasma reactors have a high technological relevance. The examples of acetylene synthesis (thermal arc plasma, plasma pyrolysis) and ozone generation (nonthermal barrier discharge) are used to illustrate both branches of plasma chemistry and explain reactor configurations.