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Objectives
1. Explain the relationship between equilibrium and changes of state
2. 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 State
solid liquid melting
solid gas sublimation
liquid solid freezing
liquid gas vaporization
gas liquid condensation
gas solid deposition
An Equilibrium Equation• Evaporation of a liquid
Liquid + energy vapor
• Condensation of a liquid
Vapor liquid + energy
• Liquid-vapor equilibrium
liquid + 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 Temperature
liquid + energy vapor
Change Shift in Equilibrium
Increase in temperature RightDecrease in temperature left
Equilibrium and Concentration
liquid + 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)
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.