Molecular Weight Surprise: N2 Bigger Than O2 & CO2

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Discussion Overview

The discussion revolves around the surprising observations made during an experiment comparing the behavior of balloons filled with carbon dioxide (CO2) and air (primarily nitrogen, N2, and oxygen, O2). Participants explore the implications of molecular weight and size on the behavior of gases, particularly in terms of buoyancy and permeability.

Discussion Character

  • Exploratory, Technical explanation, Conceptual clarification

Main Points Raised

  • One participant notes that the CO2 balloon fell faster than the air balloon due to CO2's higher molecular weight, which was unexpected given CO2's composition of two oxygen atoms and one carbon atom.
  • Another participant points out that CO2 is made of three atoms and suggests that it is smaller than O2, which consists of two oxygen atoms, although this claim is presented as interesting rather than definitive.
  • It is mentioned that CO2 can easily "dissolve" in rubbers, indicating a potential interaction with materials.
  • A later reply reiterates the size comparison, stating that CO is larger than CO2, and suggests that nitrogen (N2) is preferable for inflating balloons.

Areas of Agreement / Disagreement

Participants express differing views on the size and behavior of CO2 compared to O2 and N2, with no consensus reached on the implications of molecular size versus molecular weight.

Contextual Notes

Participants reference the permeability and kinetic size of molecules, but the discussion lacks clarity on the definitions and assumptions underlying these comparisons. Additionally, the relationship between molecular weight and behavior in gases remains unresolved.

Who May Find This Useful

Readers interested in gas behavior, molecular chemistry, and experimental physics may find this discussion relevant.

PAllen
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So, doing an experiment with my daughter (making similar size balloons filled with carbon dioxide and air), and verifying that the CO2 balloon fell quite noticeably faster due to higher molecular weight; I later noticed that the CO2 balloon shrank clearly faster than the air balloon. This was quite a surprise because CO2 is 'bigger' by weight and includes two oxygens. However, a little internet research found that permeability size is effectively the same as kinetic size, and that the size for permeability of the following molecules is exactly the inverse of their molecular weights: N2 'bigger' than O2, which is 'bigger' than CO2. For me quite a surprise, but also doubling of the value of the experiment.
 
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You teach me that CO2 molecule is made of three atoms and smaller in size than O2 which is made of two O atoms with no C. Interesting!
 
Carbon dioxide is known to easily "dissolve" in rubbers.
 
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mitochan said:
You teach me that CO2 molecule is made of three atoms and smaller in size than O2 which is made of two O atoms with no C. Interesting!
CO2 is a linear molecule, with C and O sharing electrons, maybe more towards the C.

And CO is even bigger than CO2.
Interesting indeed!

But they do say to pump up yours with N2.
 

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