Find the amount of ethanol (70 degC) in gas phase in a tank at atm

Click For Summary

Discussion Overview

The discussion revolves around calculating the amount of ethanol in the gas phase at 70 degrees Celsius in a tank at atmospheric pressure. Participants explore the application of the ideal gas law and Antoine coefficients to determine the partial pressure and moles of ethanol, as well as the mass and concentration in the vapor phase.

Discussion Character

  • Technical explanation, Mathematical reasoning, Debate/contested

Main Points Raised

  • One participant calculated the partial pressure of ethanol at 70 degrees Celsius using Antoine coefficients, resulting in a value of 0.7 bar.
  • The same participant applied the ideal gas law to find the moles of ethanol, concluding with 307 moles based on the volume of the vessel.
  • The mass of ethanol in the vapor phase was calculated to be 14130 grams, leading to a concentration of 9.42 g/liter in the gas phase.
  • Another participant questioned whether there was a specific question regarding the calculations presented.
  • A participant expressed uncertainty about the amount released, suggesting a possible misunderstanding of partial pressures.
  • One participant pointed out that the ideal gas law should use cubic meters instead of liters for volume calculations.

Areas of Agreement / Disagreement

Participants have not reached a consensus, as there are differing views on the correctness of the calculations and the application of the ideal gas law.

Contextual Notes

There is a potential limitation regarding the unit conversion in the ideal gas law, as one participant noted the need to use cubic meters instead of liters, which could affect the calculations.

warliooo
Messages
2
Reaction score
0
Homework Statement
Question: Find the amount of ethanol in gas phase in a tank blanketed by N2 at atmospheric pressure.

An empty tank of 2000 litres at atmospheric pressure and 20 degC is being used to store ethanol waste. The tank is blanketed with nitrogen, and is kept at atmospheric pressure by venting (to atmosphere).

500 litres of ethanol at 70 degrees is added to the tank. By adding 500 litres of ethanol, 500 litres of nitrogen leaves through the vent (atmospheric pressure remained).

Assuming that the ethanol in the tank reaches equilibrium in the new tank and stays at 70 degC, 1) how much ethanol will be in the gas phase within the tank? 2) if another 500 litres of ethanol is added, how much ethanol is vented to the atmosphere?
Relevant Equations
Raoults Law
I first found the partial pressure of ethanol at 70 degrees using Antoine coefficients:

Coefficients:
A
7.68117​
B
1332.04​
C
199.2​

Equation:

241016


And found a partial pressure of 0.7 bar.

This is the pressure exerted by the vapour on the liquid.

I then found the moles of ethanol at this pressure using the volume of the vessel (2000l-500l):

PV=nRT

n=PV/RT= (0.7*101325)*1500/(8.3143*(273+70))

n=307 moles

Molecular weight of ethanol = 46g/mol

1)

Mass (g) of ethanol in the vapour phase= (307*46)=14130 g

2)

Concentration of ethanol in gas phase:14130/1500=9.42 g/liter vapour

if 500 litres released: 9.42*500/1000 = 4.7 kg released.
 
Physics news on Phys.org
This all looks correct. Is there a question here?
 
The amount released seemed a bit high when I calculated it so I assumed I had made a mistake/misunderstood partial pressures. Does this seem ok to you?
 
In the ideal gas law, you should be using m^3, not liters.