State function, design a reversible process to calculate

The absolute value after entropy cannot be determined, only the change ΔS can be calculated

Only the heat temperature quotient of a reversible process can be called entropy

dS≥△Q/T ">" is used for irreversible processes "=" is reversible processes

significance

Adiabatic process: dS≥0 ">" means irreversible. "=" means reversible process

Isolated system: dS≥0 “＞” means irreversible and spontaneous “=" means reversible

Closed system: dS≥Q/T "> means irreversible "=" means reversible

Isothermal process

temperature change process

Energy degradation: The total value of energy remains unchanged but part of the energy in the system loses the ability to do work due to the increase in entropy.

The energy stored in a high-temperature object and the energy stored in a low-temperature object are the same in quantity but different in quality