The key difference between configurational entropy and thermal entropy is that configurational entropy refers to the work done without an exchange in temperature, whereas thermal entropy refers to the work done with the exchange in temperature.
In this, entropy is a measure of the randomness of a thermodynamic system. An increase in the randomness refers to the increase in the entropy and vice versa.
CONTENTS
1. Overview and Key Difference
2. What is Configurational Entropy
3. What is Thermal Entropy
4. Side by Side Comparison – Configurational Entropy vs Thermal Entropy in Tabular Form
5. Summary
What is Configurational Entropy?
Configurational entropy is the portion of a system’s entropy that is related to discrete representative positions of its constituent particles. It may describe the numerous ways the atoms or molecules in a mixture can pack together. Here, the mixtures can be alloy, glass or any other solid substance. Moreover, this term can also refer to the number of conformations of a molecule or the number of spin configurations in a magnet as well. Therefore, this term suggests that it may refer to all possible configurations of a system.
Usually, different configurations of the same substance have the same size and energy. Therefore, we can use the following relationship for the calculation of configurational entropy. It is named as Boltzmann’s entropy formula:
S=kBlnW
Configurational entropy is given by “S”, where kB is the Boltzmann constant and W is the number of possible configurations of the substance.
What is Thermal Entropy?
Thermal entropy is an extensive property of a thermodynamic system. Some things happen spontaneously, others do not. For example, heat will flow from a hot body to a cooler one, but we cannot observe the opposite even though it does not violate the law of conservation of energy. When a change occurs, the total energy remains constant but is parcelled out differently. Thus, we can determine the direction of change by the distribution of energy. Also, a change is spontaneous if it leads to greater randomness and chaos in the universe as a whole. And, we can measure the degree of chaos, randomness, or dispersal of energy by a state function; we name it as the entropy.
Figure 01: A Temperature-Entropy Diagram for Steam
The second law of thermodynamics is related to entropy, and it says, “the entropy of the universe increases in a spontaneous process.” Entropy and the amount of heat generated are related to each other by the extent to which the system uses energy. In fact, the amount of entropy change or extra disorder caused by a given amount of heat q depends on the temperature. Thus, if it is already very hot, a bit of extra heat doesn’t create much more disorder, but if the temperature is very low, the same amount of heat will cause a dramatic increase in disorder.
What is the Difference Between Configurational Entropy and Thermal Entropy?
The key difference between configurational entropy and thermal entropy is that configurational entropy refers to the work done without an exchange in temperature, whereas thermal entropy refers to the work done with the exchange in temperature. In other words, configurational entropy has no exchange in temperature while thermal entropy is based upon the change in temperature.
Below infographic summarizes the difference between configurational entropy and thermal entropy.
Summary – Configurational Entropy vs Thermal Entropy
Entropy is a measure of the randomness of a thermodynamic system. An increase in the randomness refers to the increase of the entropy and vice versa. The key difference between configurational entropy and thermal entropy is that configurational entropy refers to the work done without an exchange in temperature, whereas thermal entropy refers to the work done with the exchange in temperature.
Reference:
1. Drake, Gordon W.F. “Entropy.” Encyclopædia Britannica, Encyclopædia Britannica, Inc., 7 June 2018, Available here.
2. “Configuration Entropy.” Wikipedia, Wikimedia Foundation, 14 June 2019, Available here.
3. “Entropy.” Wikipedia, Wikimedia Foundation, 16 Mar. 2020, Available here.
Image Courtesy:
1. “Temperature-entropy chart for steam, US units” By Emok – Own work Data retrieved from: E.W. Lemmon, M.O. McLinden and D.G. Friend, “Thermophysical Properties of Fluid Systems” in NIST Chemistry WebBook, NIST Standard Reference Database Number 69, Eds. P.J. Linstrom and W.G. Mallard, National Institute of Standards and Technology, Gaithersburg MD, 20899 (retrieved November 2, 2010).) (CC BY-SA 3.0) via Commons Wikimedia