A liquid will assume the shape of its container, but has a fixed volume dependent upon temperature. Solid - Like liquids, the molecules or atoms that make up the solid are closely packed together. In chemistry we tend to ignore plasmas, leaving them to the realm of the physicists. Changes of Phase We are very familiar with materials that undergo changes of phase. Ice melts to give liquid water.
Liquid water boils to give water vapor, which is a gas.
Less commonly, dry ice sublimes from its solid directly to its vapor without passing through a liquid. Water ice can do this too, and we take advantage of this process in the important commercial process called freeze drying. We can actually measure the vapor pressure of ice as shown in the Table below, and although the values are low, they are not zero. Even at -15 o C ice has a small vapor pressure and will sublime. While we are familiar with the process of melting, but we are less familiar with the fact that pressure will affect the melting point of a material.