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# Why is the entropy of CO2 greater than O2? watch

1. My answer is, "CO2 has more bonds to vibrate, thus greater degree of disorder".

The answer sheet says, "O2 has less complex structure and therefore fewer degrees of freedom therefore less disorder".

Do you think my answer is right too?
2. (Original post by ILoveUSA)
My answer is, "CO2 has more bonds to vibrate, thus greater degree of disorder".

The answer sheet says, "O2 has less complex structure and therefore fewer degrees of freedom therefore less disorder".

Do you think my answer is right too?
You just need to hone your answer to include the complexity of carbon dioxide to include the different bends and stretches possible in the molecular vibration, i.e. degrees of freedom.
3. (Original post by ILoveUSA)
My answer is, "CO2 has more bonds to vibrate, thus greater degree of disorder".

The answer sheet says, "O2 has less complex structure and therefore fewer degrees of freedom therefore less disorder".

Do you think my answer is right too?

(Original post by charco)
You just need to hone your answer to include the complexity of carbon dioxide to include the different bends and stretches possible in the molecular vibration, i.e. degrees of freedom.
CO2 has 2 stretching modes, asymmetric and symmetric. It also has bending modes unlike O2.
4. Hi could you tell me where you found this question? Because we weren't taught how to answer something like this
5. (Original post by JMaydom)
CO2 has 2 stretching modes, asymmetric and symmetric. It also has bending modes unlike O2.
Beyond just looking at how many atoms are in the molecule (more atoms -> more degrees of freedom -> greater absolute entropy) is there any way of telling which one has more "modes" and thus higher entropy (ignoring the other factors that affect SO)? The name, perhaps, of the theories behind this field would be appreciated
Beyond just looking at how many atoms are in the molecule (more atoms -> more degrees of freedom -> greater absolute entropy) is there any way of telling which one has more "modes" and thus higher entropy (ignoring the other factors that affect SO)? The name, perhaps, of the theories behind this field would be appreciated
You need an appreciation of molecular shape (VSEPR theory, resonance, delocalisation and molecular orbital theory)

Symmetry and point group theory are more advanced ...
Beyond just looking at how many atoms are in the molecule (more atoms -> more degrees of freedom -> greater absolute entropy) is there any way of telling which one has more "modes" and thus higher entropy (ignoring the other factors that affect SO)? The name, perhaps, of the theories behind this field would be appreciated
Group theory, a branch of maths applied to chem. I don't understand it, I only know how to apply it.

One important rule is that N# of vibrational modes = 3N-6 with N the number of atoms in the molecule. This is slightly altered to 3N-5 for Linear molecules.
Beyond just looking at how many atoms are in the molecule (more atoms -> more degrees of freedom -> greater absolute entropy) is there any way of telling which one has more "modes" and thus higher entropy (ignoring the other factors that affect SO)? The name, perhaps, of the theories behind this field would be appreciated
You might be interested in this tutorial on symmetry and point group theory

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