Physical Chemistry : Identifying Intermolecular Forces

Study concepts, example questions & explanations for Physical Chemistry

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Example Questions

Example Question #1 : Identifying Intermolecular Forces

Which of the following forces is considered the weakest?

Possible Answers:

Ionic bonding

Dipole-dipole interactions

London dispersion forces

Hydrogen bonding

Correct answer:

London dispersion forces

Explanation:

The intermolecular forces from strongest to weakest are ionic, hydrogen bonding, dipole-dipole, then London dispersion forces. All compounds experience some form of London dispersion force, but the force only becomes relevant if no other forces are contributing to the attraction of molecules or atoms.

Example Question #2 : Identifying Intermolecular Forces

Which intermolecular force will be the most powerful in a sample of ethanol 

Possible Answers:

London dispersion forces

Dipole-dipole interactions

Ionic bonding

Hydrogen bonding

Correct answer:

Hydrogen bonding

Explanation:

Ethanol will not form ions in solution, so we are left with the other three options as plausible answers. Of the three, the strongest force is hydrogen bonding, which only occurs if a hydrogen is directly attached to a nitrogen, oxygen, or fluorine in the molecule. Ethanol has a hydrogen attached to an oxygen, and is thus capable of hydrogen bonding.

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