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 readily  Weak 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  ΔH v

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.

MELTING  The 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.

 H 2 O Freezes at 0 o C Melts at 0 o C

Molar Enthalpy of Fusion  The amount of energy required to melt one mole of solid at the solid’s melting point  ΔH f

Sublimation  The change of state from a solid directly to a gas  Example: dry ice (CO 2 )

Deposition  The change of state from a gas directly to a solid.  Example: frost

Phase Diagram  Figure 16; Page 347