![]() ![]() 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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