Indicate which of the following pairs will have the higher boiling point.a. CH3OH or CH3CH2CH3 b. CH4 or NH3
- Mar 3
- 2 min read
Indicate which of the following pairs will have the higher boiling point. a. CH3OH or CH3CH2CH3
b. CH4 or NH3
Solution:
The stronger the intermolecular forces, the higher the boiling point. We need to figure out the intermolecular forces for all molecules given.
Types of intermolecular forces from strongest to weakest:
Ion-Ion = exists between ions such as Na+ and Cl-. Ions are charged.
Hydrogen bonding = exists between molecules that have OH, NH or FH bonds. For example: NH3, H2O. These are strong intermolecular forces.
Dipole-dipole = exists between polar molecules. A polar molecule is asymmetrical. Example of polar molecules: NH3, HBr.
London Dispersion forces = theses intermolecular forces are present between all molecules. However, these are the only intermolecular forces between nonpolar molecules. Nonpolar molecules are symmetrical. Dispersion forces are the weakest intermolecular forces.
Now, lets look at the choices given.
a. CH3OH and CH3CH2CH3: CH3OH has hydrogen bonding because it has an OH group, CH3CH2CH3 is nonpolar (molecules that contain carbons and hydrogens only are nonpolar). CH3CH2CH3 will have London dispersion forces. Hydrogen bonding is a stronger force than London dispersion and that is why CH3OH will have a higher boiling point.
b. CH4 is nonpolar (molecules that contain carbons and hydrogens only are nonpolar) and will have London dispersion forces. NH3 has hydrogen bonding because it has OH. NH3 has stronger intermolecular forces than CH4 and will have a higher boiling point.
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