Question

Ethylene glycol has stronger intermolecular attractions than water. Do you expect the following properties to have larger or smaller valuse for ethanol when compared to water?

Vapor pressure Enthalpy of vaporization Freezing Point Viscosity

Answer 1

Both water and ethanol are covalent polar molecules.

Water and ethanol are liquids at room temperature both have intermolecular forces (IMFs) :hydrogen bonding, dipole-dipole forces and london dispersion forces are present between the molecules.

But Water have strong Hydrogen bonding compare to ethanol.

Therefore let us compare the given properties between these molecules water and ethanol

Vapor pressure:

Vapor pressure of ethanol is greater than water

As water has stronger intermolecular forces than ethanol, at a given temperature. Vapor pressure of ethanol is greater than water because number of molecules escape from liquid ethanol will be higher than water at a given temperature (strong IMFs in water). Therefore number of molecules in the vapors of ethanol will be higher than water vapor at a given temperature.

Enthalpy of vaporization:

enthalpy of vporization, the amount heat energy required to convert liquid to vapor. It means the enthalpy of vporization is the energy to break the IMFs beween the liquid molecules and make the molecules to become vapor.

As the strength of the IMFs in liquids increases, the enthalpy of vaporization values for the liquids increase.

As we have seen IMFs in liquid water is greater than ethanol, enthalpy of vaporization (deltaH_v(water)) of water is greater than enthalpy of vaporization (deltaH_v(ethanol)) of ethanol.

Freezing point:

Molecules with stronger IMFs will have higher freezing points. As we have seen that the enthalpy of vaporization of water is greater than ethanol. By cooling the liquid water freezes at a point suppose temperature be 0 deg c.

By cooling the liquid ethanol freezes at a point less further than 0 deg c. Because ethanol has weak imfs it freeze further at low temperature.

Viscosity:

Liquid which has the strong interactions or strong IMFs will have higher viscosity than liquid with weak IMFs.

So Liquid water has high viscosity than liquid ethanol.

Why H₂O has strongest inter-molecular attraction than ethanol ?

Let us look at the interactions