Shi Qi 22 Sep 2017


Two containers of volume 4.0m3 and 6.0m3 contain an ideal gas at pressures of 100Pa and 50Pa respectively. Their temperatures are equal. They are joined by a tube of negligible volume. The gas flows from one container to the other with no change in temperature. The final pressure will be

A) 70 Pa
B) 75 Pa
C) 80 Pa
D) 150 Pa


Shi Qi 20170922-1.jpg

Before the valve is opened, we first find an expression for the initial number of moles of gas in each container:

Shi Qi 20170922-2.jpg

Now, the total initial number of moles of gas can be found:

Shi Qi 20170922-3a.jpg

After the valve is opened, the pressure in each container is now the same and the temperature remains the same.

Shi Qi 20170922-4.jpg

The new expression for the final number of moles in each container is found again:

Shi Qi 20170922-5.jpg

Now, the total final number of moles of gas can be found:

Shi Qi 20170922-6.jpg

Since the total number of moles remains the same,

Shi Qi 20170922-7.jpg

Answer is A.