Two Thermally Insulated Tanks: Solving the Puzzle

[copitlory8]

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.

 

[ehild]

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

 

[copitlory8]

do i use the formula that Q=cmdeltat

 

[ehild]

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

ehild

 

[copitlory8]

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

 

[ehild]

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

 

[copitlory8]

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

 

[ehild]

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

 

[copitlory8]

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

 

[ehild]

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

 

[copitlory8]

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