Which thermodynamics concepts did Gilbert N. Lewis introduce to study real gases and concentrated solutions?

To address the limitations of existing empirical laws that only described ideal gases and dilute solutions, American chemist Gilbert N. Lewis introduced specific thermodynamic concepts to account for the behavior of real gases and concentrated solutions.

In 1901, Lewis introduced the concept of fugacity to describe the behavior of real gases. To extend these principles to concentrated solutions, he later introduced the activity coefficient in 1907. Additionally, in 1921, he introduced the concept of ionic strength, which serves as a measure of the average electrostatic interactions among ions within a solution.1

These contributions were central to his efforts to bridge the gap between thermodynamic theory and experimental practice, eventually culminating in his 1923 publication, Thermodynamics and the Free Energy of Chemical Substances.1