Calculating the volume of gas in the same canister from 2 locations.

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Discussion Overview

This discussion revolves around the calculation of gas volume in a sealed canister transported between two locations with differing atmospheric pressures and temperatures. Participants explore the implications of the ideal gas law and the discrepancies between theoretical calculations and physical measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes a scenario involving a sealed canister with a known capacity and differing ambient conditions at two locations, seeking to calculate the volume difference of gas.
  • Another participant suggests using the ideal gas law (PV=nRT) to calculate the number of moles and subsequently the volume of gas under the new conditions, noting that the assumption of no gas leakage is critical.
  • A third participant reports a calculated volume difference of approximately 154mL using the ideal gas law, which contrasts sharply with a physical measurement showing a 700mL difference, prompting questions about potential errors in calculation or measurement.
  • A later reply raises the possibility of gas leakage during transport, suggesting that changes in pressure during transport could affect the volume measurement, especially if the canister was not properly sealed.

Areas of Agreement / Disagreement

Participants express differing views on the reasons for the discrepancy between theoretical calculations and physical measurements, with no consensus reached on the cause of the significant volume difference observed.

Contextual Notes

Participants highlight assumptions related to gas leakage and the ideal gas law, indicating that real-world conditions may not fully align with theoretical models. The discussion does not resolve the mathematical steps or the implications of the differing measurements.

LAB
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I have a canister with a capacity of 8334cm3, if the canister is sealed at ambient atmospheric pressure (1016.5hPa, 25.6 deg/C) at one location then transported thousands of kilometres where the ambient pressure and temperature (1014.5hPa, 20.5 deg/C) is different.

I then connected my canister to an inverted measuring cylinder over a water bath to physically measure the difference in the volume of gas in the canister, I got a reading of -700mL (started at 1000mL finished at 300mL).

How do I mathematically calculate the difference in volume of gas in the canister in mL's ?
 
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You'd use the ideal gas law, PV=nRT
P is pressure, V is volume, n is number of molecules of substance in mols, R is the ideal gas constant (8.31 J/mol K) and T is Temperature (in Kelvin).

From the parameters you measured, you can rearrange the equation to determine the number of mols of substance in your container.
n=(PV)/(RT)

If you then want to know the volume of that container for a given pressure and temperature, you can again rearrange the equation:
V=(nRT)/P
and as long as the container remains sealed, n should remain constant.

However, this does assume that no gas was able to permeate your container (which is nearly impossible in reality).
 
Last edited:
Thank you Nessdude14,

After doing the calculation according to the Ideal Gas Laws sugested, the volume of gas at location 2 with lower temperature and pressure equals ~154mL less than location 1, but when I physically measured it; the result was 700mL less.

Can anyone sugest why this is happened? or did I calculate it in correctly?
 
How was the gas transported and in what?

If by air then gas might have leaked out due to the reduced cabin/hold pressure in flight. As you descended the increasing pressure might have resealed the container (eg gas inside now stuck at the lower cabin pressure). Hence much lower volume when measured.

If the canister is a special gas bottle then this is unlikely to be the cause - unless it wasn't sealed properly?
 

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