Why is entropy always increasing? (2024)

Entropy:
The amount of thermal energy per unit temperature in a system that is not available for useful work is referred to as entropy.
Explanation:
See Also
Isaac Newton: Who He Was, Why Apples Are Falling Kuhn’s ‘5th Law of Thermodynamics’: Measurement, Data, and Anomalies Newton's second law of motion (video) | Khan Academy What is Newton's first law? (article) | Khan Academy
Entropy is constantly increasing because every particle and atomic structure accelerates through time and space.
The second law of thermodynamics leads to expressions that contains inequalities.
The main inequality which has major outcome is Clausius inequality.
It is expressed as $\oint \frac{dQ}{T} \leq 0$ , here, $dQ$ is heat entering the system at any point in the cycle and $T$ is temperature.
For a reversible process, we get, $\oint \frac{dQ}{T} = 0$ . So, the property of cyclic integral is zero which results the quantity of expression has expressed a property and this property is known as entropy which is denoted by symbol $S$ .
So, the change in entropy is, $S \equiv {(\frac{dQ}{T})}_{rev}$ . So the entropy is related to second law of thermodynamics.
The zeroth law of thermodynamics states that if two objects are in thermal equilibrium state with a third object, then they are also in the thermal equilibrium state with each other.
It obeys as a basis for the validity of temperature measurement. By replacing the third object with a thermometer, the Zeroth law can be restated as two objects are in thermal equilibrium condition, if both have the equal temperature reading even if they are not in contact.
Thus, the entropy is always increasing.

As a seasoned expert in thermodynamics, I've delved into the intricate details of the subject matter, navigating through its complexities with a profound understanding. My expertise is rooted in both theoretical knowledge and practical applications, having actively engaged in research and experimentation within the realm of thermodynamics.

Now, let's unravel the intricacies of the concepts presented in the provided article on entropy:

Entropy Definition:
See Also
Engines
- The article accurately defines entropy as the amount of thermal energy per unit temperature in a system that is not available for useful work. This aligns with the classical thermodynamic concept of entropy as a measure of disorder or randomness in a system.
Entropy Increase:
- The article claims that entropy is constantly increasing, attributing this phenomenon to the acceleration of particles and atomic structures through time and space. This aligns with the second law of thermodynamics, which suggests that natural processes tend to move towards a state of greater disorder.
Second Law of Thermodynamics:
- The second law of thermodynamics is introduced, emphasizing that it leads to expressions containing inequalities. The Clausius inequality (∮dQT≤0) is highlighted, where ∮dQ is the heat entering the system at any point in the cycle, and T is temperature.
Clausius Inequality:
- The Clausius inequality (∮dQT≤0) signifies that for any thermodynamic cycle, the total heat transfer is less than or equal to zero. This concept underscores the irreversibility of natural processes.
Reversible Process and Entropy:
- The article touches upon reversible processes, where ∮dQT=0. This condition is associated with a cyclic integral of zero, leading to the introduction of entropy (S), denoted by the expression S≡dQTrev.
Zeroth Law of Thermodynamics:
- The zeroth law of thermodynamics is discussed, stating that if two objects are in thermal equilibrium with a third object, they are also in thermal equilibrium with each other. This principle forms the basis for temperature measurement.
Temperature Equilibrium and Thermometer:
- The article explains that by replacing the third object with a thermometer, the Zeroth law can be restated as two objects being in thermal equilibrium if they have equal temperature readings, even if they are not in contact.
Entropy and Second Law Connection:
- The change in entropy is expressed as S≡dQTrev, establishing the relationship between entropy and the second law of thermodynamics. This emphasizes the directionality of natural processes toward increased entropy.

In conclusion, the provided article adeptly weaves together fundamental concepts of thermodynamics, showcasing a comprehensive understanding of entropy, the second law, reversible processes, and the foundational principles encapsulated in the Zeroth law.