Ch 12 - Vapor Pressure & Equilibrium

Vapor pressure (Pvap)

• Def: the pressure of the vapor in equilibrium with its liquid

• Temperature relationship:

  • Higher temperature —> Higher ____

  • Lower temperature —> Lower ____

• Intermolecular forces relationship:

  • Stronger I forces —> Lower ____

  • Weaker I forces —> Higher ____

Equilibrium

• Def: the balance between the rate of vaporization and the rate of condensation

  • rate of vaporization: Liquid —> Vapor (gas)

  • rate of condensation: Vapor (gas) —> Liquid

• when these rates are equal, the total # of vapor molecules does NOT change

Higher

• Higher temperature = ______ Vapor pressure

  • @ higher temp, the molecules have more kinetic energy

    • so more of the molecules are able to escape the surface of the liquid and enter the gas phase

the vapor pressure of a certain liquid @ a certain temperature is constant, regardless of the volume of the liquid or the size/shape of the container (same temp = same Pvap)

Remember: the vapor pressure of a certain liquid @ a certain temperature is constant, regardless of the volume of the liquid or the size/shape of the container (same temp & substance = same Pvap)

when comparing two different substances, we have to look @ the strength of the intermolecular forces between the particles

Remember: when comparing two different substances, we have to look @ the strength of the intermolecular forces between the particles

lower

• Stronger Intermolecular forces = _____ vapor pressure

  • if has H-bonds then the water molecules are more strongly attracted to each other & so fewer of them will escape into the gas phase

Higher

• Weaker Intermolecular forces = ______ vapor pressure

  • Dipole attractions (just polar and NOT H-bonds)

Open container

• in an ___ _______ vapor does NOT accumulate

• Low rate of condensation compared to the rate of vaporization

• more going OUT than is coming back in

An open container will NEVER reach equilibrium (we do not compare Pvap in this case, we only compare rate of vaporization)

Remember: An open container will NEVER reach equilibrium (we do not compare Pvap in this case, we only compare rate of vaporization)

Sealed container

• in a _____ ________ the water is vaporizing @ the SAME RATE as in the open container

• vapor builds up bc of the lid and then eventually equilibrium is reached

  • rate of vaporization = rate of condensation (NO net change in the liquid level)

In a sealed container the water is vaporizing @ the SAME RATE as in the open container

Remember: In a sealed container the water is vaporizing @ the SAME RATE as in the open container

Temperature & Intermolecular forces

What are the factors that affect vapor pressure: