Problem: Three 1.0 L flasks maintained at 310K are connected to each other with stopcocks, initially closed. One flask contains 1.10 atm of N2; the second 2.25 g H2O(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

FREE Expert Solution

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 N2 after the volume change

Step 2. Calculate the pressure of H2O 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 N2 using Boyle's Law:

P1V1 = P2V2  P2 = P1V1 V2

Given:

P= 1.1 atm

V= 1.0 L (1 flask)

V= 3.0 L (3 flasks)


Also, convert to atm to torr

1 atm = 760 torr

 P2 = (1.10  atm)(1 L) (3 L)×760 mmHg1 atm

P2 = 279 torr


PN2 = 279 torr


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Problem Details

Three 1.0 L flasks maintained at 310K are connected to each other with stopcocks, initially closed. One flask contains 1.10 atm of N2; the second 2.25 g H2O(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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