How did Gilbert N. Lewis contribute to chemical thermodynamics?

Gilbert N. Lewis revolutionized chemical thermodynamics by bridging the gap between theoretical free energy models—pioneered by Josiah Willard Gibbs—and the practical, unorganized enthalpy data available at the time.1

To achieve this, Lewis pursued two primary objectives:

• Experimental Measurement: He launched a rigorous program to determine missing free-energy and entropy values, enabling more accurate thermodynamic calculations.1
• Theoretical Extension: He developed new concepts to apply empirical laws to real gases and concentrated solutions, including fugacity (1901), the activity coefficient (1907), and ionic strength (1921), which measures electrostatic interactions among ions.1

These contributions culminated in the 1923 publication of Thermodynamics and the Free Energy of Chemical Substances, co-authored with Merle Randall, which remains a landmark text in the field.1