Entropy Reduction in Expansion: Exploring Thermodynamics

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In summary: This means that the temperature and pressure will both be 1.0 Bar and 220C. Additionally, the enthalpy will be slightly lower, at 7.9kJ/(kg*K), and the entropy will be reduced as well. This process is considered spontaneous according to the second law of thermodynamics.
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jornrune
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Hi! I have a practical problem that causes me to wonder. It seems like I have to choose from gaining energy from nothing, or to get a reduction in entropy from a spontaneous process.

Imagine a small enclosed chamber filled with dry H2O gas. The properties are:
0.5 Bar
8.0 kJ/(kg*K)
200C
2850kJ/kg

An infinitely large reservoir of H2O gas has the following properties:
1.0 Bar
8.0kJ/(kg*K)
240C
2950kJ/kg

Here is a reference chart:
http://www.steamtablesonline.com/images/steam tables p-h diagram (large).png

A valve between the large reservoir and the small chamber is opened and the two gasses are mixed until they reach equilibrium inside the chamber and the pressure is stabilized at 1 bar. Am I correct in assuming that no work has been done and that the properties will be as follows?:
1.0 Bar
7.9kJ/(kg*K)
220C
2900kJ/kg

This seems to be correct as far as temperature and pressure goes. It also seems to add up with the enthalpy as the process is thought to be adiabatic. However, the entropy is lowered, and the process seems to be a so called spontaneous process. The question is if this goes along with the second law of thermodynamics. (It can be read here if you need it refreshed: http://en.wikipedia.org/wiki/Second_law_of_thermodynamics)

Also, I see no room for different results. The pressure is given by the infinite source. This means we can not leave the 1 bar line. There is no way we can get any condensation, so we have the following options:
1: The entropy is actually reduced
2: Enthalpy is lost or gained, and so is temperature

...or am I overlooking something here?

Thanks for any response!
 
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  • #2
If you open up the valve and wait for equilibrium, the gas inside your small chamber will be identical to the one in the large reservoir.
 

Related to Entropy Reduction in Expansion: Exploring Thermodynamics

1. What is entropy reduction in expansion?

Entropy reduction in expansion refers to the decrease in disorder or randomness of a system as it expands. This is a concept in thermodynamics, which is the study of energy and its transformations.

2. How does entropy reduction occur during expansion?

Entropy reduction occurs during expansion when a system releases energy and becomes more ordered. This is because as the system expands, its molecules have more space to move and arrange themselves in a more organized manner.

3. What is the relationship between entropy reduction and temperature?

Entropy reduction is directly related to temperature. As temperature decreases, the disorder of a system decreases, resulting in entropy reduction. Conversely, as temperature increases, the disorder and entropy of a system also increase.

4. Why is studying entropy reduction important?

Studying entropy reduction is important because it helps us understand how energy is transformed and how systems reach equilibrium. It also has practical applications in fields such as engineering and chemistry, where understanding and controlling entropy can lead to more efficient processes.

5. Can entropy reduction be reversed?

In most cases, entropy reduction cannot be reversed. This is due to the second law of thermodynamics, which states that the total entropy of a closed system will always increase over time. However, in certain scenarios, such as in living organisms, entropy reduction can occur temporarily through the input of external energy sources.

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