Types

• Density is a measure of mass per unit volume. Solids have a constant density, and the density of liquids is fairly constant; the density of a gas, on the other hand, can change. Chlorine gas, therefore, has a density that is not always the same.
  
  

Function

• Chlorine molecules are large enough that the ideal gas law (PV = nRT) is a less-than-perfect description of its behavior. While the van der Waals equation offers a more accurate description, the ideal gas law is much more straightforward, and is thus a reasonable approximation for simple calculations. The molar mass of Cl2 is about 71 grams, so 71 grams of chlorine equals 1 mole of chlorine. Given these numbers, we can estimate the volume of a specific mass of chlorine at a given temperature and pressure using PV = nRT, where P is pressure, V is volume, n is number of moles, R is the ideal gas constant and T is temperature. Once we have the volume, we divide the mass by the volume to find the density.
  
  

Considerations

• At high pressure or at temperatures below its boiling point of -39.15 degrees Celsius or -38.47 degrees Fahrenheit, chlorine can form a liquid. According to the book "Chemical Principles, the Quest for Insight," by Peter Atkins and Loretta Jones, the density of liquid chlorine is 1.66 grams per cubic centimeter, or 1.73 ounces per fluid ounce.