DRAFT: This module has unpublished changes.

The purpose of this lab is to determine how the intermolecular interactions affect the physical properties of Ethanol and Acetone.

 

There are three interactions that affect the physical properties of substances and solutions, which are known as Van Der Waals interactions. The interactions are dipole-dipole, ion-dipole, and London type dispersion forces. The dipole-dipole forces exist between two dipole molecules, such as water molecules and ethanol molecules. Ion-dipole forces exist between ions and polar molecules, such as Na+ ions and water molecules in a solution of NaCl. The London dispersion forces are attractions between and instantaneous dipole and an induced dipole. These are present in all molecules, whether they are polar or nonpolar and are rather weak because they are only temporary and occur rapidly. The bond strength between molecules is determined by the melting point, boiling point, and vapor pressure of a substance at a given temperature.

 

The greater the bond strength, the higher the melting and boiling point since more thermal energy is going to be used to break the bonds. The greater the strength between molecules the lower the vapor pressure because at a given temperature fewer molecules will posses the necessary kinetic energy to escape the gas phase. The last factor affecting molecular interactions is the size of the molecules.         

 

The mathematical relationship between the heat of vaporization and the temperature is expressed by the Clausius-Claperyon equation:

 ln p=- ((ΔHvap)/RT) +C

 

p= vapor of the substance

ΔHvap= heat of vaporization (J/mol)

T= temperature (K)

C= a constant

R= 8.314 J/(mol K)

DRAFT: This module has unpublished changes.