AN ideal gas is useful construct from a theoretical perspective. It permits us think about many phenomena without the complxity of including intermolecular interactions or the finite size of molecules. Most of the useful expressions that we derive are based on the ideal gas equation of state. While engeineers who are designing chemical reactors may need the corrections for the real gas it turns out that we can use the ideal gas law for many calculations at moderate pressure (even higher than atmospheric pressure) without a significant error or loss of accuracy. Thus, a asecond reason for definintg and using an ideal gas is practical. It is the simplest model and it works. Models of real gases must begin somewhere. We need a framework and the ideal gas law also gives us that starting poitn for corrections that will form a theory of real gases.

A look at the units for pressure and energy

Pressure is defined as a force per unit area. It is crucial to understand pressure at a molecule level in order to fully understand the concept of an ideal gas. In the video below we briefly treat the definition of pressure and units used to describe it. The work done by chemical processes involves pressure-volume changes. Thus, we also consider the units of that work and how they relate to Joules. This uni conversions are definitions are an important foundation for solving problems in thermodynamics.