Calculate the mass of propane that has been used

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Homework Help Overview

The problem involves calculating the mass of propane gas used from a cylinder under varying pressure conditions. The cylinder's dimensions and the gas's molar mass are provided, along with initial and final gauge pressures and a constant temperature.

Discussion Character

  • Exploratory, Assumption checking, Mathematical reasoning

Approaches and Questions Raised

  • Participants discuss the application of the ideal gas law and the relationship between pressure, volume, and temperature. There is an attempt to calculate the mass of propane based on initial and final pressures, but concerns about the accuracy of calculations and assumptions regarding the number of moles are raised.

Discussion Status

Some participants are verifying calculations and questioning the assumptions made in the equations used. There is acknowledgment of potential errors in mathematical execution, particularly regarding significant figures and volume calculations. No consensus has been reached on the final mass calculation, but there is a collaborative effort to clarify the approach.

Contextual Notes

Participants note the importance of significant figures in the calculations and the assumption that the number of moles may change due to gas being burnt, which affects the applicability of certain equations.

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Homework Statement



A cylinder 1.00 m tall with an inside diameter of 0.120 m is used to hold propane gas (molar mass: 44.1 g.mol-1) for use in a barbeque. It is initially filled with a gas until the gauge pressure is 1.30 x 10^7 Pa and the temperature is 22.0⁰C. The temperature of the gas remains constant as it is partially emptied out of the tank, until the gauge pressure is 2.50 x 10^5 Pa. Calculate the mass of propane that has been used.

Homework Equations



1.. pV = nRT
2.. p1V1 / T1 = p2V2 / T2

The Attempt at a Solution



I am really wrong here but just need a guiding hand...

The volume of the cylinder is 0.11309733m^3
From Eq 1 I get the number of moles = 60 then total mass = 60 x 44.1 = 2643.64g
Then did this again for pressure 2 (2.5 x 10^5 Pa) to get = 50.84g
Difference being 2592.8g of gas used but this seems large.

I then looked at Eq 2 and I got V2 = 0.588m^3
Not really sure where to go with that...
 
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Second equation assumes number of moles of gas have not changed - so it is of no use, some of the gas was burnt.

Your first approach looks OK, just check your math again. Mass difference is much larger than you think. Seems like you have problems with position of the decimal point.
 
Hi Borek,

I typed that wrong! It should be 0.011309733m^3

The final value of 2592.8g was calculate from that figure. So is this what you get?
 
Obviously when it comes to calculating volume of cylinder I am not better than you

Your result is OK, just watch significant figures.

--
 
LOL, thanks heaps Borek.
 

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