ABSTRACT
The common states of matter are solids, liquids, and gases. This chapter introduces the difference between the terms state (solid, liquid, and gas) and phase (a particular state with a constant chemical composition) and then considers different states of matter in turn. The properties of each state – density and arrangement of particles – highlight the differences between condensed (solid and liquid) phases compared to gases. The dispersed nature of gases makes the physical property density (mass per volume) less useful than it is for solids and liquids, where density varies little with temperature. The Ideal Gas Law is introduced as a tool for relating the amount and volume of a gas as it varies with temperature and pressure. After discussing states of matter, readers are introduced to the terminology and energetics of phase changes. The impact of temperature and pressure in exerting physical changes, phase changes, is discussed along with the use of pressure-temperature diagrams to represent these relationships. The chapter concludes with a discussion of dissolving and the differences between ionic compounds (which dissociate) and molecular compounds (which do not dissociate).
