How does water vapor affect the expansion of butane in a lighter?

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Discussion Overview

The discussion centers on the expansion of butane from a liquid state to a gas state within a lighter, exploring the principles of gas laws, pressure dynamics, and experimental measurements. Participants inquire about the underlying theories and laws governing this process, as well as the implications of water vapor's presence in the measurements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Experimental/applied

Main Points Raised

  • One participant questions how butane expands from liquid to gas, seeking explanations involving relevant laws or theories.
  • Another participant references the ideal gas law (PV=NkT) to highlight the density differences between liquid and gas states.
  • There is a discussion about measuring mass changes during the phase transition, with one participant suggesting the combined gas law might be applicable.
  • A participant explains that the pressure inside the lighter is slightly higher than atmospheric pressure, affecting the equilibrium between liquid and vapor states.
  • One participant shares an experimental observation involving a butane lighter underwater, noting discrepancies in calculated molar mass and seeking insights into potential experimental errors.
  • Another participant prompts for clarification on the volume measurement of the gas and the importance of correcting for standard temperature and pressure (STP).
  • Concerns are raised about the presence of water vapor affecting the molecular mass calculations, with a participant asking how to express the mole fraction of water vapor algebraically.

Areas of Agreement / Disagreement

Participants express various viewpoints on the principles governing the expansion of butane and the impact of water vapor on measurements. There is no consensus on the experimental errors or the exact implications of water vapor's presence, indicating ongoing uncertainty and exploration.

Contextual Notes

Participants mention the need for corrections in volume measurements to STP and the potential influence of water vapor on molecular mass calculations, suggesting that these factors may complicate the experimental results.

kateman
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i was interested if anyone could explain how a butane lighter can expand from liquid state into the gas state with what appears to be, more volume?

it'd be great if you could mention any laws or theories

thanks :)
 
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PV=NkT

Liquid is denser than gas.
 
thanks

any way/formula of measuring the mass when it changes?

would the combined gas law work in this instance?
 
You can measure the mass change with a scale, but the density of the liquid you can probably just google.
 
kateman said:
i was interested if anyone could explain how a butane lighter can expand from liquid state into the gas state with what appears to be, more volume?

it'd be great if you could mention any laws or theories

thanks :)
It's a matter of reduced pressure. Inside the lighter casing/reservoir, the pressure is slightly higher than atmospheric pressure. The liquid/vapor inside is satured, such that the pressure is fixed according to temperature. When a little vapor is released (because of the pressure differential between inside and out), more liquid becomes vapor to maintain an equilibrium.

Outside the lighter, the pressure is 1 atm.

See -
http://www.engineeringtoolbox.com/propane-butane-mix-d_1043.html (annoying popups on this site).
Propane is more suited to colder environments since it evaporates at -44°F (-42°C) at atmospheric pressure. Butane evaporates at 33°F (-0.5°C) at atmospheric pressure.

The vapor pressure of a mixture of the two products can be found in the table below:
 
thank-you Astronuc, that is exactly what i was after
one more quick question, i did an experiment of using a butane lighter underwater and collecting the gas in an inverted cylinder so that the butane gas displaces the water and from there finding the molar mass of butane.

Well the lighter lost 0.04 grams of butane yet there were 101ml of gas in the cylinder. I worked it out (assuming butane is an ideal gas, which its not) so that butane had a molar mass of 9.46g (which is way off).
The working is right, so what could my experimental error could have been?
 
How was the volume of the gas measured? Also, make sure volume measurements are corrected to STP.

Reweigh the lighter.

Also, was the volume dry or was water vapor present. A significant mole fraction of water vapor would drop the molecular mass.

The molar mass is ~58 g/mole.

The density of the gas is 2.52 g/l or 0.00252 g/ml, so with 101 ml, one should have 0.255 g, so one is off somewhere by a factor of about 6.
 
the volume of gas was measured by finding the amount of water left in the inverted cylinder and taking it off the total capacity of the cylinder.

water vapor was present. it was taken of the room pressure to give the butane pressure.


"A significant mole fraction of water vapor would drop the molecular mass."
how would find the volume of water vapor in the cylinder and express that mole fraction algebraically?
 

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