Two Thermally Insulated Tanks: Solving the Puzzle

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Homework Help Overview

The discussion revolves around a problem involving two thermally insulated tanks containing neon gas, connected by a valve. The participants are tasked with determining the final temperature and pressure after the valve is opened, while considering the conservation of energy and the properties of gases.

Discussion Character

  • Exploratory, Assumption checking, Conceptual clarification

Approaches and Questions Raised

  • Participants explore the conservation of quantities during the mixing of gases, questioning how to apply thermodynamic principles and the ideal gas law. There are discussions about specific heat capacities, the mass of the gas, and the implications of changing conditions upon opening the valve.

Discussion Status

The conversation is ongoing, with participants attempting to clarify their understanding of the ideal gas law and internal energy calculations. Some guidance has been provided regarding the use of the ideal gas law and the need to consider the total volume and moles of gas after the valve is opened, but no consensus has been reached on the specific calculations required.

Contextual Notes

Participants note the lack of specific information regarding the mass of the neon gas and the conditions under which the specific heat capacities are defined. There is an emphasis on the constraints of the problem, such as the assumption of no energy exchange with the surroundings and the thermally insulated nature of the tanks.

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The drawing shows two thermally insulated tanks. drawing: http://www.webassign.net/CJ/14_26.gif
They are connected by a valve that is initially closed. Each tank contains neon gas at the pressure, temperature, and volume indicated in the drawing. When the valve is opened, the contents of the two tanks mix, and the pressure becomes constant throughout.

(a) What is the final temperature? Ignore any change in temperature of the tanks themselves.(Hint: The heat gained by the gas in one tank is equal to that lost by the other.)
_______K
(b) What is the final pressure?
_______Pa
I have stared at this picture for like 30 minutes and read the entire chapter on thermodynamics in my physics book but I can't find a solution. Please provide one, thank you.
 
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Find quantities which are conserved during the experiment for this system of two tanks. Opening the valve will not change the overall volume. The gas does not escape. There is no exchange of energy with the surroundings...

ehild
 


do i use the formula that Q=cmdeltat
 


If you know m and c and Q... Do you know them?

ehild
 


i think i should answer yes, however i don't know the mass of neon gas. is it going to be the molecular mass?
 


You can not answer yes. In principle, the specific heat capacity is given either for constant volume or for constant pressure. If you look at the data, the gas in the tanks is at different pressure. When the valve is opened, some gas flows from one tank to the other, so the volume of the gas changes, and so does its pressure.

Use the ideal gas law to find the amount of gas in both tanks.

ehild
 


well the ideal gas law is pv=(m/M)RT and R=8.31 but how do i use this equation
 


Use the form with moles, n : pV=nRT. You know p, V and T for both tanks you can calculate the number of moles they contain.

ehild
 


okay so after i get the moles in each tank what do i do?
 
  • #10


After opening the valve you have one container with volume equal to the sum of both tanks, and the amount of gas equal to the sum of the moles initially present in both tanks. You can write the idel gas law for this container, too.

You can do the same with the internal energy. It is the sum of the initial internal energies of both tanks.

ehild
 
  • #11


now you lost me. i don't know how to calculate the internal energy give just the moles
 

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