## Practice Midterm W18 #3A

Volume: $\Delta S = nR\ln \frac{V_{2}}{V_{1}}$
Temperature: $\Delta S = nC\ln \frac{T_{2}}{T_{1}}$

DianaTrujillo2K
Posts: 40
Joined: Fri Sep 29, 2017 7:04 am

### Practice Midterm W18 #3A

Can someone please explain how I would go about solving this problem?

It reads: Lex Luthor finds a sealed box that has two compartments. He puts 9.00g of Helium gas in the first compartment, and 125g of Krypton gas in the second. The compartment with Krypton is 3 times the size of the compartment with Helium (triple the volume). He then removes the separating divider, allowing the gases to mix, and sees that temperature then increases from 50.0 to 75.0 degrees C.
Assuming the gases are ideal monoatomic gases throughout the process, what is the total change in entropy of the system?

Andres Reynoso 1J
Posts: 30
Joined: Fri Sep 29, 2017 7:06 am

### Re: Practice Midterm W18 #3A

Essentially, you would solve for the entropy at each individual step then add the totals up; this can be done because entropy is a state function.
Your first step would to be to calculate the change in entropy due to the change in volume of helium gas. Step two would be to calculate the entropy change associated with the change in volume of Krypton gas. Finally, you would calculate the entropy change for the change in the system's temperature.

Step 1: $\Delta S_{1}=nRln\frac{V_{2}}{V_{1}}$
Step 2: $\Delta S_{2}=nRln\frac{V_{2}}{V_{1}}$
Step 3: $\Delta S_{3}=nCln\frac{T_{2}}{T_{1}}$
Step 4: $\Delta S_{tot}=\Delta S_{1}+\Delta S_{2}+\Delta S_{3}$

Hopefully this helps!