Question

A 265 ml flask conrtaines pure helim art a poressure of 749 torr. A 455 ml flask contains pure argon at a pressure of 729 torr. The two flasks are connected through stopcock and are at the same temperature. What is the pressure once the stopcock is opened?

a. 736 Torr
b. 276 Torr
c. 461 Torr
d. 250 Torr

Answer 1

To calculate the final pressure in the combined flask system, Dalton's Law of Partial Pressures is applied, along with using Boyle's Law to conserve moles of gas. The correct calculation yields a final pressure of 736 torr.

Step-by-step explanation:

To find the final pressure in the combined system of helium and argon gases, we can use Dalton's Law of Partial Pressures, which states that the total pressure exerted by a mixture of non-reacting gases is equal to the sum of the partial pressures of individual gases. We can consider each flask to be at the same temperature since it is stated that they are at the same temperature before they are connected.

First, we take the pressures of the individual gases in their respective flasks:

• Helium in a 265 mL flask at 749 torr
• Argon in a 455 mL flask at 729 to

Next, we calculate the total volume when the two flasks are connected:
Total Volume = 265 mL + 455 mL = 720 mL

We then find the partial pressures considering the conservation of moles before and after the connection since no additional gas is added or removed, and the number of moles changes only due to the change in volume according to Boyle's Law, where P1V1 = P2V2 for a given gas:

1. For helium:
2. For argon:
   Finally, we add the partial pressures to get the final pressure:Final Pressure = P2 of helium + P2 of argo

Calculating the above gives us the final pressure as 736 torr, which corresponds to choice (a