Ethanol, C2H5OH, and carbon dioxide, CO2, have approximately the same molecular

Question

Ethanol, C2H5OH, and carbon dioxide, CO2, have approximately the same molecular weight, yet carbon dioxide is a gas at STP and ethanol is a liquid. How do you account for this difference in physical property?

Ethanol, C2H5OH, and carbon dioxide, CO2, have approximately the same molecular weight, yet carbon dioxide is a gas at STP and ethanol is a liquid. How do you account for this difference in physical property?

Ethanol, C2H5OH, and carbon dioxide, CO2, have approximately the same molecular weight, yet carbon dioxide is a gas at STP and ethanol is a liquid. How do you account for this difference in physical property?

Explanation / Answer

The difference has to do with the intermolecular forces between the molecules of each substance.

Ethanol has a water-like structure with hydrogen bonding being prominent in its liquid state. Hydrogen bonds are strong interactions between molecules. That means that the molecules in the liquid phase are harder to break apart into the vapor phase compared to those compounds that do not have hydrogen bonding capabilities.

CO2 is a non-polar molecule so the only real force between molecules will be van der Waals forces which are quite weak. The fact that the forces are weak (compared to hydrogen bonding) means that the compound will have a much lower boiling point and melting point than molecules of similar molecular weights.

Hope this is helpful to you.

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