Gases are perhaps the best understood of the three states of matter.
Chapter five touches all of the important bases as far as the study of gases is concerned. An Overview of the Physical States of Matter Gases are different from liquids and solids in that they expand to fill the entire container in which they are confined. Gases, as opposed to liqujids and solids, are also highly compressible, thermally expandable, have low viscosities and low densities, and are highly miscible with other gases. Measuring the Pressure of a Gas Pressure is defined as force per unit area, barometers are devices used to measure atmospheric pressure, and manometers are devices used to measure the pressure of a gas involved in a lab experiment. As far as pressure is concerned, chemists refer primarily to two sets of units.