Changes of States of Matter

Abstract

It is a fact of life in our daily experience and was a real enigma for a century– pure matter dramatically changes at extremely precise temperatures. In the nineteenth century, pioneering scientists, from Gay-Lussac to Van der Waals, carried out meticulous measurements of the fluid state, paving the way for microscopic descriptions which underlie our natural sciences today. The study of properties of gases at low density enabled the introduction of absolute temperature as a measure of the kinetic energy of molecules. The striking generality of thermal behaviour and mechanical properties of gases with vastly varying chemical properties was thereby elucidated. Thermodynamics and its microscopic interpretations was born on the wave of this success. However the pioneers of fluid observations also tackled liquid–vapour transformations and discovered another elegant generality which was far from evident a priori: In a dilute gas, molecules are almost isolated and therefore one thinks their chemical properties are unimportant, but what about in a liquid where the molecules are in constant interaction?