thermodynamics

The branch of physics governing energy transfer as heat and work, and the evolution of entropy.

• zeroth law: thermal equilibrium defines temperature
• first law: energy is conserved — heat in equals work out plus internal energy change
• second law: entropy of an isolated system never decreases
• third law: entropy approaches zero as temperature approaches absolute zero
• free energy determines spontaneous processes and equilibrium
• connects mechanics at the microscopic scale to macroscopic observables
• underpins chemistry, biology, and information theory