Is entropy a state function12/15/2023 ![]() ![]() In other words, time reversibility is fulfilled if the process happens the same way if time were to flow in reverse or the order of states in the process is reversed (the last state becomes the first and vice versa). The reversibility of thermodynamics must be statistical in nature that is, it must be merely highly unlikely, but not impossible, that a system will lower in entropy. While the fundamental theoretical laws of physics are all time-reversible, experimentally the probability of real reversibility is low and the former state of system and surroundings is recovered only to certain extent (see: uncertainty principle). Thermodynamics defines the statistical behaviour of large numbers of entities, whose exact behavior is given by more specific laws. ( Learn how and when to remove this template message) ( April 2014) ( Learn how and when to remove this template message) There might be a discussion about this on the talk page. This section may be confusing or unclear to readers. Absolute versus statistical reversibility Whereas a single enzyme was once believed to catalyze both the forward and reverse chemical changes, research has found that two separate enzymes of similar structure are typically needed to perform what results in a pair of thermodynamically irreversible processes. ![]() Many biological processes that were once thought to be reversible have been found to actually be a pairing of two irreversible processes. This energy will not be recoverable if the process is reversed. ![]() During this transformation, there will be some heat energy loss or dissipation due to intermolecular friction and collisions. Some "transformation energy" will be used as the molecules of the "working body" do work on each other when they change from one state to another. The phenomenon of irreversibility results from the fact that if a thermodynamic system, which is any system of sufficient complexity, of interacting molecules is brought from one thermodynamic state to another, the configuration or arrangement of the atoms and molecules in the system will change in a way that is not easily predictable. One of the reasons that Diesel engines are able to attain higher efficiency is that the combustion is much more uniform, so less energy is lost to dissipation and the process is closer to reversible. Obviously, this is not true and there is a flame front and sometimes even engine knocking. As another example, to approximate the expansion in an internal combustion engine as reversible, we would be assuming that the temperature and pressure uniformly change throughout the volume after the spark. Thus, if the system is always uniform, then the process is reversible, meaning that you can return the system to its original state by either adding or removing heat, doing work on the system, or letting the system do work. Then dissipation would occur the temperature distribution would become uniform with no work being done, and this would be irreversible because you couldn't add or remove heat or change the volume to return the system to its initial state. This is just the same as if in a system one section of the gas was hot, and the other cold. For dissipation to occur, there needs to be such a non uniformity. Initially, there is part of the system with gas in it, and part of the system with no gas. For example, Joule expansion is irreversible because initially the system is not uniform. Intuitively, a process is reversible if there is no dissipation. The second law of thermodynamics can be used to determine whether a hypothetical process is reversible or not. An irreversible process increases the total entropy of the system and its surroundings. However, the impossibility occurs in restoring the environment to its own initial conditions. Because entropy is a state function, the change in entropy of the system is the same whether the process is reversible or irreversible. A system that undergoes an irreversible process may still be capable of returning to its initial state. In thermodynamics, a change in the thermodynamic state of a system and all of its surroundings cannot be precisely restored to its initial state by infinitesimal changes in some property of the system without expenditure of energy. melting of ice cubes in water) is well approximated as reversible. All complex natural processes are irreversible, although a phase transition at the coexistence temperature (e.g. This concept arises frequently in thermodynamics. In science, a process that is not reversible is called irreversible. ![]()
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