# 98044537 - Second Law of Thermodynamics The Second Law of Thermodynamics describes the behavior of isolated systems: systems that exchange neither matter nor energy with their surroundings. It has two main statements: the first talks about the direction of energy transfer, and the second is about entropy. ## ☝️ Key Points - The Second Law of Thermodynamics applies to isolated systems. - The first statement establishes that heat naturally flows from hot to cold objects; heat can't flow naturally from cold to hot objects. - The second statement establishes that every energy transformation increases the entropy of an isolated system. - The Second Law has several applications, including engines, refrigerators, and heat pumps. ## 📑 Content ### The First Law of Thermodynamics Before we dive into the Second Law of Thermodynamics, let's first understand the First Law, which says that energy cannot be created or destroyed; it can only be converted from one form to another. This means that the total amount of energy in a system is constant. ### The Second Law of Thermodynamics The Second Law differentiates between reversible and irreversible processes. In a reversible process, a system can be returned to its initial state by modifying every factor that has affected it. An example of a reversible process is a pendulum swinging back and forth with no friction. However, when friction is included, the process is irreversible because the energy lost due to friction cannot be converted back perfectly into the original energy. ### Entropy Entropy is a measure of the amount of disorder in a system. Entropy was initially introduced to measure the amount of useful energy in a system that is not available to do work. The Second Law establishes that for every energy transformation, the entropy of an isolated system must increase. This notion can be understood by observing heat transfer. Heat naturally flows from hot to cold objects, and it has never been observed for heat to flow naturally from a cold object to a hot object. ### Applications The second law has several applications in the real world, including engines, refrigerators, and heat pumps. An engine is a device that converts heat into work; for an engine to work, there must be a temperature difference between a hot engine and a cooler environment. Refrigerators and heat pumps use energy to move heat from cold to hot environments; this process is called a heat pump cycle. ## 📚 Resources - [Hyperphysics: Second Law of Thermodynamics](http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/seclaw.html) - [MIT OpenCourseWare: Second Law of Thermodynamics](https://ocw.mit.edu/courses/physics/8-01-physics-i-classical-mechanics-fall-1999/lecture-notes/chapter15.pdf) ## 🔗 References - Callen, Herbert B. *Introduction to Thermodynamics and Thermostatistics*. New York: Wiley, 1985. - Atkins, Peter, and Julio de Paula. *Physical Chemistry*. Oxford: Oxford University Press, 2006. ### Further reading - [Wikipedia: Second Law of Thermodynamics](https://en.wikipedia.org/wiki/Second_law_of_thermodynamics) - [Khan Academy: Second Law of Thermodynamics](https://www.khanacademy.org/science/physics/thermodynamics/laws-of-thermodynamics/a/the-second-law-of-thermodynamics) ### Backlinks - [[First Law of Thermodynamics]] - [[Entropy]] - [[Thermodynamics]] **🏷️ Tags:** #topic/physics #topic/thermodynamics #type/wiki