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The intermolecular forces between $\ce{CO2}$ molecules are dispersion forces, while the forces between $\ce{CO}$ molecules are mostly dipole-dipole attraction forces. So, why does $\ce{CO2}$ have a higher boiling point than that of $\ce{CO}$?

Todd Minehardt
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Lyndt
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  • related http://chemistry.stackexchange.com/questions/42946/can-nonpolar-molecules-exhibit-dipole-dipole-forces – Mithoron Jan 16 '16 at 18:40
  • I don't think it answers my question. – Lyndt Jan 16 '16 at 18:53
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    There are many other points on the scale from dipole-dipole interaction to dispersion forces. $\ce{CO}$ is a very weak dipole; on the other hand, $\ce{CO2}$ is a pretty strong quadrupole. – Ivan Neretin Jan 16 '16 at 19:23
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    the forces between COCO molecules are mostly dipole-dipole attraction forces. || Orientation of CO molecules in solid is random with weak preference of head-tail. This suggests that dispersion interactions dominates in CO solid.

     – permeakra Jan 17 '16 at 11:20
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    Also the MW of $\ce{CO2}$ is about 57% greater than that of $\ce{CO}$ meaning that it will take considerably more energy to raise the kinetic energy of the heavier molecule to where it has the necessary surface escape velocity. – ron Jan 17 '16 at 19:38
  • CO$_2$ does cannot exist at a liquid under standard conditions, but CO can. CO$_2$undergoes sublimation and only exists in liquid form at high pressures so it is inaccurate to compare the boiling points if they are not under the same pressure. – Ryan Jan 22 '16 at 19:01

2 Answers2

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$\ce{CO2}$ has more electrons than $\ce{CO}$. This means that it has a much larger electron cloud as compared to $\ce{CO}$, so its more easily polarised and thus, the ease of forming instataneous dipole-induced dipole bonds increases. Even though $\ce{CO}$ is a polar molecule and it forms permanent dipole-permanent dipole bonds, in this case the id-id bonds are stronger.

P.s. Just a $17 \space year \space old$ A Level Chem student here, I might be wrong

ADITYA DAS
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Rish
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The larger the small covalent molecule, the greater the intermolecular bonds, hence higher boiling / melting point.

$\ce{CO2}$ has 3 atoms involved in the molecule and is therefore larger than $\ce{O2}$ that has 2 atoms. Hence, $\ce{CO2}$ has a higher boiling / melting point compared to $\ce{O2}$. (Exception to this is water molecules.)

tschoppi
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Ramila Patel
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