2 Change Of State PowerPoint

Change in States of Matter

Definitions

• Phase: Uniform part of a system (solid, liquid, gas).

• Condensation: Gas to liquid transition.

• Vapor: Gas in contact with its liquid/solid phase.

• Equilibrium: Opposing changes occur at equal rates in a closed system.

Vapor Pressure

• Affected by:

  • Change in concentration

  • Change in temperature

  • Change in pressure

• Equilibrium Vapor Pressure: Pressure exerted by vapor at given temperature in equilibrium with liquid.

Types of Liquids

• Volatile Liquids: Evaporate easily, weak attractions.

• Nonvolatile Liquids: Do not evaporate easily, strong attractions.

Energy Changes in Changes of State

• Energy involved in physical/chemical changes.

• Law of Conservation of Energy: Energy can be absorbed/released, never created or destroyed.

• Forms of energy: Heat, light.

Vaporization Processes

• Vaporization: Liquid to gas change.

  • Boiling: At liquid's surface and within.

  • Evaporation: At liquid's surface.

• Boiling Point: Temperature where vapor pressure equals atmospheric pressure.

• Normal Boiling Point (n.b.p.): Boiling point at standard pressure (1 atm).

Heat of Vaporization

• Energy needed to boil 1 g of liquid at boiling point (Water: 2260 J/g).

• Calculation: q = mHvap

Heat of Fusion

• Energy required to melt 1 g of solid at melting point (Water: 334 J/g).

• Calculation: q = mHfus

Energy Transfer During Phase Changes

• Endothermic: Requires energy (e.g., vaporization and melting).

• Exothermic: Releases energy (e.g., condensation and freezing).

Sublimation and Deposition

• Sublimation: Solid to gas.

• Deposition: Gas to solid.

Phase Diagrams

• Graph of temperature vs. pressure showing phases of a substance.

• Triple Point: All three phases in equilibrium.

• Critical Point: Conditions beyond which a substance cannot exist as a liquid.

Key Points from the Phases of Water

• Freezing Point: 0°C.

• Normal Boiling Point: 100°C.