Understanding Helmholtz Free Energy: Get Heat for Free?

In summary: Therefore, the system has reached thermal equilibrium with the environment. In summary, the Second Law of Thermodynamics explains that heat can enter a system from the environment due to an increase in entropy, which allows for more microstates and thus a rise in temperature. When a system absorbs exactly TΔS of heat, it reaches thermal equilibrium with the environment.
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I'm having some trouble understanding this concept. Why is it that you sometimes can get heat for free from the environment? Like suppose you have a system, on which you make an energyconsuming proces which creates entropy. Then you subtract TΔS because apparently heat can enter when the entropy increases - why is that? Does the temperature drop, when we increase the entropy?
Can you guys please explain in terms of microstates too, as it is that way I feel I understand it the best.
Also, how do you know that the temperatures between the environment and the system is the same AFTER it has absorbed exactly TΔS?
 
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Heat can enter a system from the environment because of the Second Law of Thermodynamics. This law states that entropy always increases over time, and that the entropy of an isolated system can never decrease. Entropy is related to the number of microstates available for a given macrostate. As the entropy of a system increases, so does its number of microstates. The increase in microstates allows energy to enter the system from the environment, resulting in an increase in temperature. When a system absorbs exactly TΔS of heat from the environment, the temperatures between the environment and the system are the same AFTER the transfer of heat. This is because the amount of heat transferred is equal to the temperature difference multiplied by the entropy change. Since the temperatures are now equal, there is no longer a temperature difference between the two and therefore no more heat can be transferred.
 

Related to Understanding Helmholtz Free Energy: Get Heat for Free?

1. What is Helmholtz Free Energy?

Helmholtz Free Energy is a thermodynamic potential that measures the maximum amount of work a system can perform at a constant temperature and volume. It takes into account the internal energy of a system as well as its entropy.

2. Why is Helmholtz Free Energy important?

Helmholtz Free Energy helps us understand the behavior of systems at a constant temperature and volume. It allows us to determine whether a process is spontaneous or not, and how much useful work can be extracted from the system.

3. How is Helmholtz Free Energy calculated?

Helmholtz Free Energy is calculated using the equation F = U - TS, where F is the Helmholtz Free Energy, U is the internal energy of the system, T is the temperature, and S is the entropy. The units for Helmholtz Free Energy are Joules (J).

4. Can Helmholtz Free Energy be negative?

Yes, Helmholtz Free Energy can be negative. A negative Helmholtz Free Energy indicates that the system has the potential to do work and that the process is spontaneous. This is known as an exergonic process.

5. How can we use Helmholtz Free Energy to "get heat for free"?

Helmholtz Free Energy can be used to determine the maximum amount of work that can be extracted from a system at a constant temperature and volume. This work can then be converted into heat, providing a source of "free" heat energy.

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