Why is entropy not conserved in 1st law of thermodynamics?

This is why entropy is not conserved, even though internal energy is. In summary, the first law of thermodynamics states that internal energy is conserved, but entropy is not because it is related to the number of possible microstates in a system and can change during a process.
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Homework Statement


The first law of thermodynamics is about the conservation of internal energy. Why is
entropy not conserved?

Homework Equations



dU = dq + dwexp + dw, where dwe is work in addition (e for ‘extra’) to the expansion work, dwexp.

The Attempt at a Solution


In thermodynamics, the total energy of a system is called its internal energy, U. The
internal energy is the total kinetic and potential energy of the molecules in the system.
We denote by ∆U the change in internal energy when a system changes from an initial
state i with internal energy Ui to a final state f of internal energy U. A molecule has a certain number of motional degrees of freedom, such as the ability
to translate (the motion of its centre of mass through space), rotate around its centre
of mass, or vibrate (as its bond lengths and angles change, leaving its centre of mass
unmoved). Entropy is also related to "freedom" but i couldn't understand the relationship between entropy and 1st law of thermodynamics.
 
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Answer: Entropy is not conserved because it is a measure of the disorder or randomness in a system. It can change during a process, even when the internal energy remains constant. This is because entropy is related to the number of different possible microstates that a system can be in. As a system changes, the number of possible microstates can change as well, leading to a change in entropy.
 

Related to Why is entropy not conserved in 1st law of thermodynamics?

1. Why is entropy not conserved in the 1st law of thermodynamics?

The first law of thermodynamics states that energy cannot be created or destroyed, only converted from one form to another. However, this law does not include the concept of entropy, which is the measure of disorder in a system. This means that while energy may be conserved, the level of disorder in a system can still change.

2. What is the relationship between entropy and the 1st law of thermodynamics?

The 1st law of thermodynamics and entropy are both fundamental principles in thermodynamics, but they are not directly related. While the 1st law deals with energy conservation, entropy deals with the distribution of that energy within a system. A change in entropy does not necessarily mean a change in energy, and vice versa.

3. How does the 1st law of thermodynamics account for changes in entropy?

The 1st law does not explicitly account for changes in entropy, but it does acknowledge that energy can be transferred and transformed, leading to changes in entropy. For example, when energy is converted from one form to another, some of that energy may be lost as heat, increasing the overall entropy of the system.

4. Can entropy be created or destroyed?

No, entropy cannot be created or destroyed. It can only change in value. This is in line with the 1st law of thermodynamics, which states that energy cannot be created or destroyed. However, the 2nd law of thermodynamics states that entropy will always tend to increase in a closed system, as energy becomes more dispersed and less organized.

5. How does the 2nd law of thermodynamics relate to the concept of entropy?

The 2nd law of thermodynamics states that the total entropy of a closed system will always tend to increase over time, leading to a state of maximum entropy or disorder. This is because energy will naturally disperse and become less organized, leading to an increase in entropy. Therefore, the 2nd law is closely related to the concept of entropy and explains why it is not conserved in the 1st law of thermodynamics.

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