If a reversible process occurs, there is no net change in entropy. The second law of thermodynamics can be stated in terms of entropy.
For a thermodynamic system involved in a heat transfer of size Q at a temperature T, a change in entropy can be measured by: Although it's difficult to measure the total entropy of a system, it's generally fairly easy to measure changes in entropy. This is the ultimate level of disorder if everything is at the same temperature, no work can be done, and all the energy will end up as the random motion of atoms and molecules.Ī measure of the level of disorder of a system is entropy, represented by S. The second law also predicts the end of the universe: it implies that the universe will end in a "heat death" in which everything is at the same temperature. One of the most important implications of the second law is that it indicates which way time goes - time naturally flows in a way that increases disorder. Many processes are irreversible, and any irreversible process increases the level of disorder. A pendulum will gradually lose energy and come to a stop, but it doesn't pick up energy spontaneously an ice cube melts to form a puddle, but a puddle never spontaneously transforms itself into an ice cube a glass falling off a table might shatter when it hits the ground, but the pieces will never spontaneously jump back together to form the glass again. If you watched a film forwards and backwards, you would almost certainly be able to tell which way was which because of the way things happen. This applies to anything that flows: it will naturally flow downhill rather than uphill. One implication of the second law is that heat flows spontaneously from a hotter region to a cooler region, but will not flow spontaneously the other way. Systems tend to move from ordered behavior to more random behavior.
The second law - The level of disorder in the universe is steadily increasing. The second law of thermodynamics is one of the most fundamental laws of nature, having profound implications. Entropy and the second law Entropy and the second law
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