Positive deviation from Raoult’s Law
- The solute- solute and solvent-solvent interaction are stronger than solute-solvent interaction.
- Let pA = Partial vapour pressures of component A
PB = Partial vapour pressures of component B
Hmix = Change in enthalpy of mixing.
Vmix =Change in volume of mixing.
- pA > pAoxA
- pB > pBoxB
- ΔHmix > 0
- ΔVmix > 0
- Total vapor pressure is more than as expected from Raoult’s law.
- Solution of ethanol and acetonebehaves in the same manner. Molecules of pure ethanol are hydrogen bonded. The molecules of acetone get in between the molecules of ethanol on addition of acetone and break some of the hydrogen bonds between them.
