Liquids and Solids

Changes of State

Objectives1. Explain the relationship between equilibrium

and changes of state2. Define Le Chatelier’s Principle.3. Predict changes in equilibrium using Le

Chatelier’s Principle.

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EquilibriumEquilibrium – a dynamic state in which two opposing

changes occur at equal rates in a closed system.

Changes of Statesolid liquid meltingsolid gas sublimationliquid solid freezingliquid gas vaporizationgas liquid condensationgas solid deposition

An Equilibrium Equation• Evaporation of a liquid

Liquid + energy vapor

• Condensation of a liquidVapor liquid + energy

• Liquid-vapor equilibriumliquid + energy vapor

Le Chatelier’s Principle

A system at equilibrium will shift to offset a stress or change in conditions

imposed on the system.

Equilibrium and Temperatureliquid + energy vapor

Change Shift in EquilibriumIncrease in temperature RightDecrease in temperature left

Equilibrium and Concentrationliquid + energy vapor

Change Shift in EquilbriumAddition of liquid RightRemoval of liquid LeftAddition of vapor LeftRemoval of vapor Right

Decrease in container volume LeftIncrease in container volume right

Equilibrium Vapor Pressure• Pressure exerted by a vapor in equilibrium

with its corresponding liquid at a given temperature

-an increase in temperature causes an increase in equilibrium vapor pressure; result of increased K.E. of the liquid particles.

Volatile and Non-volatile liquids• Volatile Liquid – a liquid that

readily evaporates at room temp.; liquids with low intermolecular forces.

BoilingBoiling……occurs when the equilibrium vapor pressure of a

liquid equals the atmospheric pressure…conversion of a liquid to a vapor within the liquid as

well as at the surface.

Normal Boiling Point: boiling point at standard atmospheric pressure (100oC for water)

Boiling

Energy and Boiling

Molar Heat of Vaporization• The amount of energy needed to vaporize

1 mole of a liquid at its boiling point

Freezing and MeltingFreezing:

Liquid solid + heat energy

Melting: Solid + heat energy liquid

Normal freezing point: temperature at which a solid and liquid are at equilbrium at standard pressure (0oC for water

Molar Heat of Fusion – energy required to melt one mole of a solid at its melting point.

Phase Diagram

Triple Point – temperature and pressure conditions at which the solid, liquid, and gas phases of a substance can coexist at equilibrium

Critical temperature - temperature above which a substance cannot exist in the liquid phase.

Critical pressure – the lowest pressure at which a substance can exist as a liquid at the critical temperature.

Phase Diagram for CO2