The primary difference between liquids and gases is that the constituent molecules of liquids are closer together and move less than those that make up gases. Liquids and gases behave in a number of similar ways, although both differ greatly from solids.
While gas molecules move freely past one another, those in liquids slide against one another. While both liquids and gases take on the shape of their containers, a gas contains fewer molecules than a similar quantity of liquid. While it is easy to compress most gases, it requires considerably more force to compress a liquid, and some liquids cannot be compressed at all.
The temperature, pressure and volume that a substance is exposed to determine the state it takes. In most daily situations, the atmospheric pressure remains constant, so the biggest determining factor is the temperature of a substance. Technically, temperature measures the speed at which the molecules in a substance are moving. The faster the molecules are moving, the more spaced out they become. For example, water takes a gaseous state at temperatures above 212 degrees Fahrenheit, is a liquid between 33 and 211 degrees Fahrenheit and turns into a solid at or below 32 degrees Fahrenheit.