Chapter 10, Section 4

Changes of State

Phase

Any part of a system that has uniform composition and properties.

Condensation

Process by which a gas changes to a liquid

Equilibrium

Dynamic condition Two opposing changes occur at equal rates in a closed system

Equilibrium Vapor Pressure

The pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature.

Volatile Liquids

Evaporate readilyWeak forces of attraction between their particles.

Example: ether

BOILING:

Vaporization (appearance of bubbles) throughout a liquid.

BOILING POINT

The temperature at which the vapor pressure of the liquid is just equal to the atmospheric pressure.

Molar Enthalpy of Vaporization

Amount of energy needed to vaporize one mole of liquid at the liquid’s boiling point at constant pressure

ΔHv

FREEZING: The physical change of a

liquid to a solid by removal of energy as heat.

As a liquid cools, the KE decreases & particles are pulled together in a more orderly arrangement – a solid.

FREEZING POINT

The temperature at which the solid & liquid are in equilibrium at 1 atm (atmosphere) of pressure.

MELTINGThe opposite of freezing

The physical change of a solid to a liquid by the addition of energy.

The melting and freezing points for a substance are at the same temperature.

H2OFreezes at 0oCMelts at 0oC

Molar Enthalpy of Fusion

The amount of energy required to melt one mole of solid at the solid’s melting point

ΔHf

Sublimation

The change of state from a solid directly to a gas

Example: dry ice (CO2)

Deposition

The change of state from a gas directly to a solid.

Example: frost

Phase Diagram

Figure 16; Page 347