What happens to entropy when mixing two gases with different properties?

In summary, this student is asking if the entropy is lowered when the pressure is stabilized at 1 bar. The student is correct in assuming that the entropy is lowered.
  • #1
jornrune
4
0
Hi, I am new here, so please direct me if I am posting completely wrong here.

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
Is there anyone here who would like to share their opinion?
 
  • #3
I thought this was an easy one... Should I expect more response if it was posted in the Classical Physics section?
 

FAQ: What happens to entropy when mixing two gases with different properties?

1. What is final entropy of gas mixture?

The final entropy of a gas mixture is a measure of the disorder or randomness of the gas molecules in the mixture after they have reached equilibrium. It is a thermodynamic property that quantifies the distribution of energy and the level of disorder in the system.

2. How is final entropy of gas mixture calculated?

The final entropy of a gas mixture can be calculated using the equation S_final = ∑(n_iRln(V_i/V_total)), where n_i is the number of moles of each gas component, R is the gas constant, and V_i and V_total are the volumes of each gas and the total volume of the mixture, respectively.

3. What factors affect the final entropy of gas mixture?

The final entropy of a gas mixture is affected by various factors, including temperature, pressure, volume, and the number of gas molecules present. It also depends on the type of gas molecules and their individual entropies.

4. Can the final entropy of gas mixture decrease?

According to the second law of thermodynamics, the final entropy of a gas mixture cannot decrease in an isolated system. However, it is possible for the entropy to decrease in a non-isolated system if energy is transferred or work is done on the system.

5. What is the significance of final entropy of gas mixture in real-world applications?

The final entropy of a gas mixture is an important concept in many real-world applications, such as in chemical reactions, industrial processes, and energy systems. It helps to understand the direction and efficiency of these processes, and it also plays a role in predicting the behavior of gases in different conditions.

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