From Earth to Titan by way of the laboratory: what do we know about pressure?

Chemistry is often said to have originated with the discovery of fire, and thus it follows that the most important agent for carrying out chemical reactions has commonly been (with the possible exception of reactions in the gas stage) temperature. However, knowledge of chemical balance requires that we bear in mind the three thermodynamic variables: pressure, temperature and composition. With respect to this balance, therefore, pressure is a variable that is just as important as the others and thus it is well-known, for example, that a system so close to us and as complex as our planet is, like all planets, a chemical system in which pressure plays a determining role. This is reflected in the compositional evolution of the materials present on Earth in progression toward the Earth's centre, since pressure and temperature increase the nearer one gets to the centre. In this lecture, the speaker will examine the essential, though not exclusively, in its structural aspect. Thus he will analyse the changes that take place in packings, coordination indices, oxidation states, etc, which are basically reflected in two main types of processes: phase transitions and chemical reactions. Through these, the speaker will describe a few examples of the synthesis of materials in conditions of high pressure and high temperature. As they are materials, particular attention will be paid to the physiochemical properties of the products of these processes.