Gases Gases, collective term for one of the three visibly different states of ordinary matter, liquid and solid being the other two. Solids have well-defined shapes and are difficult to compress. Liquids are free-flowing and bounded by self-formed surfaces. Gases expand freely to fill their containers and are much lower in density than liquids and solids. The atomic theory of matter defines states, or phases, in terms of order. Molecules have a certain freedom of …showed first 75 words of 249 total…

…showed last 75 words of 249 total…the pressure. Charles's law, or Gay-Lussac's law, states that if a gas is held at a constant pressure the volume is directly proportional to the absolute temperature. Combining these laws gives the ideal gas law: PV/T = R (per mole), also known as the equation of state of an ideal gas. The constant R on the right-hand side of the equation is a universal constant, the discovery of which is a cornerstone of modern science.