1824 — Carnot: Sadi Carnot publishes "Reflections on the Motive Power of Fire" — establishes that maximum efficiency of a heat engine depends only on the temperatures of heat source and sink. Foundation of the second law.

1843 — Joule: James Prescott Joule experimentally establishes the mechanical equivalent of heat ($1\ \text{cal} = 4.186\ \text{J}$). Demonstrates that heat is a form of energy.

1850 — Clausius: Rudolf Clausius formulates the first and second laws mathematically. Introduces the concept of "equivalence-value" (later named entropy).

1865 — Clausius: Names the new concept "entropy" (from Greek "tropē" meaning transformation). States: "The entropy of the universe tends toward a maximum."

1876-1878 — Gibbs: Josiah Willard Gibbs publishes "On the Equilibrium of Heterogeneous Substances" — introduces Gibbs free energy, chemical potential, and phase rule. This single work establishes most of chemical thermodynamics.

1884 — Van't Hoff: Jacobus Van't Hoff derives the equation $\frac{d\ln K}{dT} = \frac{\Delta H}{RT^2}$ connecting equilibrium constants to thermodynamics.

1900-1905 — Nernst: Walther Nernst formulates the third law: entropy of a perfect crystalline substance at 0 K is zero. Later used to derive absolute entropies.

1923 — Lewis and Randall: Gilbert Lewis introduces the concept of "activity" and refines the relationship $\Delta G^\circ = -RT\ln K$ for real systems.

Modern usage: IUPAC standardizes sign conventions (work done ON system positive), used in NCERT and taught in NEET preparation.$