We are asked to** calculate the total pressure after the stopcocks were opened. **

**Opening the stopcock will essentially change the volume for each component.**

- The pressure of the gas will adjust to the volume according to the ideal gas law.
- Now the vapor pressures will not change as long as there is enough liquid that could evaporate and adjust to maintain the vapor pressure.

**We go through the following steps to solve the problem: **

**Step 1. **Calculate the pressure of N_{2} after the volume change

**Step 2.** Calculate the pressure of H_{2}O if all of it evaporated and compare to the vapor pressure.

**Step 3.** Calculate the pressure of ethanol if all of it evaporated and compare to the vapor pressure.

**Step 4.** Calculate the total pressure.

**Step 1.**Calculate the pressure of N_{2} using Boyle's Law:

$\overline{){{\mathbf{P}}}_{{\mathbf{1}}}{{\mathbf{V}}}_{{\mathbf{1}}}{\mathbf{}}{\mathbf{=}}{\mathbf{}}{{\mathbf{P}}}_{{\mathbf{2}}}{{\mathbf{V}}}_{{\mathbf{2}}}{\mathbf{}}}\phantom{\rule{0ex}{0ex}}\mathbf{}{\mathbf{P}}_{\mathbf{2}}\mathbf{}\mathbf{=}\mathbf{}\frac{{\mathbf{P}}_{{\mathbf{1}}}{\mathbf{V}}_{{\mathbf{1}}}\mathbf{}}{{\mathbf{V}}_{\mathbf{2}}}$

Given:

**P _{1 }= 1.1 atm**

**V _{1 }= 1.0 L (1 flask)**

**V _{2 }= 3.0 L (3 flasks)**

**Also, convert to atm to torr**

**1 atm = 760 torr**

$\mathbf{}{\mathbf{P}}_{\mathbf{2}}\mathbf{}\mathbf{=}\mathbf{}\frac{\mathbf{(}\mathbf{1}\mathbf{.}\mathbf{10}\mathbf{}\mathbf{}\overline{)\mathbf{atm}}\mathbf{)}\mathbf{(}\mathbf{1}\mathbf{}\overline{)\mathbf{L}}\mathbf{)}\mathbf{}}{(3\overline{)L})}\mathbf{\times}\frac{\mathbf{760}\mathbf{}\mathbf{mmHg}}{\mathbf{1}\mathbf{}\overline{)\mathbf{atm}}}$

**P _{2} = 279 torr**

**P _{N2} = 279 torr**

Three 1.0 L flasks maintained at 310K are connected to each other with stopcocks, initially closed. One flask contains 1.10 atm of N_{2}; the second 2.25 g H_{2}O(l); and the third, 0.450 g of ethanol(l), FW 46.1 g/mol. The vapor pressure of water at 310K is 43 torr and that of ethanol is 104 torr. When the stopcocks are opened and the contents mix freely, what is the final total pressure in torr?

A. 385 torr

B. 1705 torr

C. 836 torr

D. 806 torr

E. 551 torr

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