Entropy Change
Entropy Change - Related Videos
03:00
Standard Entropy Change for a Reaction
0 Views •
2020
Entropy is a state function, so the standard entropy change for a chemical reaction (ΔS°rxn) can be calculated from the difference in standard entropy between the products and the reactants. where np and nr represent the stoichiometric coefficients in the balanced equation of the products and reactants, respectively. For example, ΔS°rxn for the following reaction at room temperature is computed as follows: A partial listing of standard entropies is provided in the table. Substance
01:10
Entropy Change in Reversible Processes
0 Views •
2023
In the Carnot engine, which achieves the maximum efficiency between two reservoirs of fixed temperatures, the total change in entropy is zero. The observation can be generalized by considering any reversible cyclic process consisting of many Carnot cycles. Thus, it can be stated that the total entropy change of any ideal reversible cycle is zero. The statement can be further generalized to prove that entropy is a state function. Take a cyclic process between any two points on a p-V diagram.
07:32
Entropy
0 Views •
2023
Source: Ketron Mitchell-Wynne, PhD, Asantha Cooray, PhD, Department of Physics & Astronomy, School of Physical Sciences, University of California, Irvine, CA The second law of thermodynamics is a fundamental law of nature. It states that the entropy of a system always increases over time or remains constant in ideal cases when a system is in a steady state or undergoing a "reversible process." If the system is undergoing an irreversible process, the entropy of the system will always...
02:39
Entropy
0 Views •
2020
Salt particles that have dissolved in water never spontaneously come back together in solution to reform solid particles. Moreover, a gas that has expanded in a vacuum remains dispersed and never spontaneously reassembles. The unidirectional nature of these phenomena is the result of a thermodynamic state function called entropy (S). Entropy is the measure of the extent to which the energy is dispersed throughout a system, or in other words, it is proportional to the degree of disorder of a...
01:18
Entropy
0 Views •
2023
The first law of thermodynamics is quantitatively formulated via an equation relating the internal energy of a system, the heat exchanged by it, and the work done on it. A quantitative formulation of the second law of thermodynamics leads to defining a state function, the entropy. When an ideal gas expands isothermally, the disorder in the gas increases. From the molecular perspective, the gas molecules have more volume to move around in. Consider an infinitesimal step in the expansion, which...
FAQs
For a reversible change, entropy change is obtained from the heat transferred reversibly divided by temperature, expressed as dS = δQ_rev/T. An irreversible process does not follow that idealized path and produces entropy. This distinction allows physicists to separate entropy associated with controlled heat transfer from entropy generated by irreversibility during a real process.
An isolated system cannot exchange energy or matter with its surroundings, so any entropy produced internally remains part of the system’s total entropy. Its entropy therefore stays constant for an ideal reversible process or increases when the process is irreversible. This rule supplies a thermodynamic direction for natural change and helps identify whether a proposed process is feasible.
Temperature sets the scale for converting reversible heat transfer into entropy change through dS = δQ_rev/T. For a given amount of reversible heat, the associated entropy change depends on the temperature at which transfer occurs. Tracking that temperature dependence connects measurable macroscopic heat exchange with the system’s changing energy dispersal and microscopic arrangements.
First identify the initial and final states, including the relevant temperature and heat-transfer information. Then evaluate the entropy change using a reversible path between those states, applying dS = δQ_rev/T along that path. This approach is useful even when the actual process is irreversible because the entropy change can still be determined from the state-to-state analysis.
Entropy change provides a thermodynamic test for whether heat transfer or a phase transition can occur in the indicated direction. Analysis compares the entropy associated with the initial and final states and checks the total behavior of an isolated system. The result can distinguish a feasible change from one that would conflict with the requirement that total entropy cannot decrease.
For chemical reactions and other physical processes, entropy change helps evaluate thermodynamic feasibility rather than describing only temperature or heat separately. Its connection to accessible microscopic arrangements clarifies why systems can move toward equilibrium and why irreversible changes have a preferred direction. Consequently, entropy provides a bridge between macroscopic thermodynamic measurements and microscopic physical behavior.