Heat

The heat, Q is given by

$\delta Q=TdS$

where T is the temperature and S is the entropy. $\delta$ represents an inexact differential, indicating that the resulting value depends on the path taken. This equation is an equality when the process is reversible, i.e., the system evolves through a succession of equilibrium states. If the process is irreversible one has

$\delta Q<TdS$

See also

• First law of thermodynamics
• Second law of thermodynamics
• Heat flow

References

Related reading

• Leonard K. Nash "Reversible and irreversible heating and cooling", Journal of Chemical Education 47 pp. 357-361 (1970)