PX154 - E3 - the second law of thermodynamics

• this is a macroscopic law: obeyed by statistically significant number of particles
• it is an empirical law that has never been observed to fail

kelvine-planck

• "it is impossible for any system to undergo a process in which it absorbs heat from a reservoir at a single temperature and converts the heat completely into mechanical work, with the system ending in the same state in which it began"
  
• an engine takes in heat energy, $Q_H$, and does work, $W$. it is impossible for there to be zero waste heat, $Q_C$ expelled to the cold reservoir
• basically, $ϵ\ne 100\mathrm{\%}$

clausius

• heat transfer from cold to hot never happens spontaneously