How to Calculate Gas Volume When Given Mass?

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Discussion Overview

The discussion revolves around calculating the volume of gas produced from a given mass, specifically focusing on sulfur dioxide in the context of a chemistry problem. It includes considerations of standard temperature and pressure (STP) and the ideal gas law, as well as the implications of using approximations in calculations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Homework-related

Main Points Raised

  • One participant asks how to calculate the volume of sulfur dioxide formed from a specific mass of copper.
  • Another participant states that at STP, 1 mole of any gas equals 22.4L, suggesting that multiplying the moles of sulfur dioxide by 22.4L gives the volume.
  • A different participant cautions that using 22.4L assumes conditions at STP, which lacks a universally accepted definition, and emphasizes the ideal gas equation (pV=nRT) as a more general approach.
  • One participant expresses gratitude for the information and acknowledges the need to memorize the constant 22.4L, indicating a basic understanding of the topic.
  • Another participant defends the use of shortcuts and simplifications in learning, noting the importance of recognizing them as such.
  • A participant questions whether multiplying 22.4L by the number of moles is sufficient for high-school level chemistry, suggesting a preference for not learning the ideal gas equation at this stage.
  • Another participant reiterates that if STP is defined as 22.4L per mole, then multiplying by the number of moles is a reasonable approximation unless exact conditions are provided.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of using the 22.4L constant and the ideal gas equation. While some support the use of the constant as a simplification, others highlight the potential pitfalls of relying solely on it without understanding the underlying principles.

Contextual Notes

There are unresolved issues regarding the definition of STP and the assumptions made when using the ideal gas law versus the 22.4L shortcut. The discussion reflects varying levels of familiarity with the concepts involved.

MadmanMurray
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I had a question on a test which asked me the volume of sulphur dioxide that would be formed if 12.7g of copper were used. How do you calculate gas volume when you only have the mass?
 
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At STP, 1 mol of any gas is equal to 22.4L. So if you know the moles of sulfur dioxide you can multiply that by 22.4 to get the volume.
 
That's assuming you are asked for volume at STP and assuming you know what STP means. STP has no one, accepted definition and T/p values used depend on the application, defining body and so on. See wikipedia article on STP for details.

The most general approach is to use ideal gas equation, pV=nRT. Using 22.4L is only a shortcut, one that can give dangerously wrong answer.
 
Thanks a lot Renge. I knew it was a constant I just couldn't find the constant on google. I best memorize that number.

Borek this is real basic chemistry we're doing at the moment the teacher wrote that constant (22.4L) on the board I just forgot it. It was STP I forgot to mention that. I'm going to learn that ideal gas equation though because chemistry is the field I'm planning on getting into. Thanks.
 
There is nothing wrong with using some shortcuts and simplifications at some point when learning an idea, it is just good to know beforehand that it is just a simplification.
 
I have a question related to this thread. So if the STP of any gas is 22.4L per mole, all you have to do is to multiply 22.4L with the number of moles of the specified gas? High-school level chemistry is what I'm doing, so as of right now I need not learn that equation...
 
Julian_delia said:
So if the STP of any gas is 22.4L per mole

VOLUME of 1 mole of gas at STP is 22.4L.

all you have to do is to multiply 22.4L with the number of moles of the specified gas?

If you are not given exact conditions (T,P) that's often the best approximation.
 

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