Colligative Properties

Explain freezing-point depression and boiling-point elevation at the molecular level. Additional KEY Terms Colligative Properties

Vapour Pressure / Boiling point / Freezing point Colligative Properties: Physical properties of solutions that are affected by the number (not identity) of solute particles dissolved. Vapour Pressure / Boiling point / Freezing point

Remember: particles at the surface have fewer IMFs. Vapour pressure: Pressure of vapour at equilibrium with its liquid in a closed container. evaporation = condensation Remember: particles at the surface have fewer IMFs.

Fewer particles evaporate = LESS V. PRESSURE solutes take up space and prevent solvent particles from reaching surface. Fewer particles evaporate = LESS V. PRESSURE

More energy needed to boil = HIGHER BP Boiling point: temperature needed for vapour particles to have pressure equal to air pressure for escape. solutes take up space and prevent solvent particles from getting close to the heat source. More energy needed to boil = HIGHER BP

Freezing point: temperature needed for liquid particles to lose energy and phase change to solid. Na Na Cl solutes take up space and prevent solvent particles from forming crystalline structure. Difficult to form solids = LOWER FP Particles must ‘slow down’ more to connect to each other.

CAN YOU / HAVE YOU? Explain freezing-point depression and boiling-point elevation at the molecular level. Additional KEY Terms Colligative Properties