The Clausius statement of the second law of thermodynamics asserts that it is impossible for a self-acting machine, unaided by any external force, to transfer heat from a cooler body to a hotter one. This principle underlines the unidirectional nature of spontaneous heat transfer.
Second Law of Thermodynamics: A fundamental principle stating that total entropy always increases over time for an isolated system.
Kelvin-Planck Statement: An alternative formulation of the second law, asserting that no process can convert all absorbed heat into work without any other effect.
Entropy: A measure of disorder or randomness in a system, often increasing in natural processes according to the second law.