Real Gasses

We want to correct the Ideal Gas Law, which only works well with high temperature and low pressure.

Correction #1: molecules do in fact occupy space:

where is the reciprocal of molarity ()

Correction #2: Intermolecular forces of attraction between molecules lowers the pressure

where is a constant with units , which describes the strength of intermolecular attraction proportional to the squared concentration of molecules.

Equation

When a gas isn't ideal, Van der Wall's equation is a more accurate formula to use:

Example

Five systems are described below. The temperature of each system is . Rank them in order as to how well they will be described by the ideal gas law.

  • at
  • at
  • at
  • at
  • at

solution

  1. at because helium is smaller, it takes up less space
  2. at
  3. at
  4. at
  5. at
Example

Four systems are described below. The pressure of each system is . Rank them in order as to how well they will be described by the ideal gas law.

  • at
  • at
  • at
  • at

solution

  1. at
  2. at
  3. at
  4. at
Example

One mole of occupies a volume of and and . Identify whether each of the following statements is true or false:

  1. behaves like an ideal gas
    • False
  2. The density of is less than the density predicted by the ideal gas law
    • False, since , and ideal gas law predicts greater volume
  3. The molecules are attracting each other
    • True