There are multiple valid ways to state the second law of thermodynamics. Some ways of expressing the law do so in terms of macroscopic notions such as heat and temperature.
Other descriptions employ the concept of entropy, which is based upon a statistical approach to thermodynamics. Some alternative macroscopic statements include:
- There can be no process with the sole result of absorbing heat and completely converting it into work.
- It is impossible to convert heat completely into work in a cyclic process.
- It is impossible to carry out a cyclic process using an engine connected to two heat reservoirs that will have as its only effect the transfer of a quantity of heat from the low-temperature reservoir to the high-temperature reservoir.
- The entropy of a closed system must increase or remain the same.
- For any irreversible process, the entropy of a system and its surroundings must increase; for a reversible process, the entropy of a system and its surroundings must remain the same.
A convenient way to remember the laws or thermodynamics is:
- First Law: You cannot win.
- Second Law: You cannot break even.
- Third Law: Let's keep score, or alternatively: you cannot leave the game.
- Atkins, P. W. Physical Chemistry, W. H. Freeman and Company, New York, 3rd edition, 1986
- McQuarrie, Donal d A., Statistical Thermodynamics, University Science Books, Mill Valley, CA, 1973
- Bromberg, J. Philip, Physical Chemistry, Allan and Bacon, Inc., Boston, 2nd Edition, 1984
- Wikipedia: The Second Law of Thermodynamics
- Anderson, H.C., Stanford University, Lectures on Statistical Thermodynamics, ca. 1990.
- What the Second Law Does Not Say
- What the Second Law Does Say
- Entropy is Not a Measure of Disorder
- Reversible Processes
- The Carnot Cycle
- The Definition of Entropy
- Perpetual Motion
- The Hydrogen Economy
- Heat Can Be Transferred From a Cold Body to a Hot Body: The Air Conditioner
- The Second Law and Swamp Coolers
- Entropy and Statistical Thermodynamics
- Partition Functions
- Entropy and Information Theory
- The Second Law and Creationism
- Entropy as Religious, Spiritual, or Self-Help Metaphor
- Free Energy
- Spontaneous Change and Equilibrium
- The Second Law, Radiative Transfer, and Global Warming
- The Second Law, Microscopic Reversibility, and Small Systems
- The Arrow of Time
- The Heat Death of the Universe
- Gravity and Entropy
- The Second Law and Nietzsche's Eternal Recurrence