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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.
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.
Changes in entropy (ΔS), together with changes in enthalpy (ΔH), enable us to predict in which direction a chemical or physical change will occur spontaneously. Before discussing how to do so, however, we must understand the difference between a reversible process and an irreversible one.
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.
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.
Define entropy. Calculate the increase of entropy in a system with reversible and irreversible processes. Explain the expected fate of the universe in entropic terms. Calculate the increasing disorder of a system.
Many earlier textbooks took the approach of defining a change in entropy, ΔS, via the equation: ΔS = Q reversible /T (i) where Q is the quantity of heat and T the thermodynamic temperature. However, it is more common today to find entropy explained in terms of the degree of disorder in the system and to define the entropy change, ΔS, as:
