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For the expansion (or compression) of an ideal gas from an initial volume and pressure to a final volume and pressure at any constant temperature, the change in entropy is given by: Here is the amount of gas (in moles) and is the ideal gas constant.
28 Νοε 2021 · Entropy is a measure of the randomness or disorder of a system. Its symbol is the capital letter S. Typical units are joules per kelvin (J/K). Change in entropy can have a positive (more disordered) or negative (less disordered) value. In the natural world, entropy tends to increase.
The change in entropy of a system for an arbitrary, reversible transition for which the temperature is not necessarily constant is defined by modifying \(\Delta S = Q/T\). Imagine a system making a transition from state A to B in small, discrete steps.
As before, the change in entropy can be calculated from the definition of \(\Delta S\) once we find the energy \(Q\) needed to melt the ice. Solution The change in entropy is defined as: \[\Delta S = \dfrac{Q}{T}.\]
The change in entropy is positive, because heat transfers energy into the ice to cause the phase change. This is a significant increase in entropy, because it takes place at a relatively low temperature.
13 Νοε 2022 · A change is said to occur reversibly when it can be carried out in a series of infinitesimal steps, each one of which can be undone by making a similarly minute change to the conditions that bring the change about.
The definition refers to the reversible transfer of energy as heat. A reversible process is one that changes direction when an external variable, such as pressure or temperature, is changed by an infinitesimal amount. In a reversible process, the system and its surroundings are in equilibrium.
