Phase Changes There are six main state changes They are all physical changes! The identity of the substance stays the same!

Phase ChangesThere are six main state changesThey are all physical changes!The identity of the substance stays the same!

I. Freezing and MeltingA. Freezing: change from

liquid to solidFreezing point: the temperature at which a liquid becomes a solid

B. Melting: change from solid to liquid

Melting point: the temperature at which a solid becomes a liquid

II. Evaporation and CondensationA. Evaporation: change

from liquid to gasBoiling point: the temperature at which a liquid changes into gas

B. Condensation: change from gas to liquid

III. Deposition and SublimationA. Sublimation: change

from solid to gasThe thin film of ice on the windshield going away

B. Deposition: change from gas to solid

Frost on the grass

IV. Energy in State ChangesA. The energy of rapid random

motion of atom sized particles1. All matter has energy related to this2. Energy increases and temperature

increasesAs energy is added the particles move

more rapidlyThe more rapid the movement the state can be overcome

V. TemperatureA. If the state is overcome the

temperature stops changing because the energy is being used to change the state of the substance

B. Temperature remains constant throughout a state change • as long as there is some of both states

the temperature DOES NOT CHANGE!!

VI. Endothermic & ExothermicA.Endothermic

Heat required (enters the system)

Melting: solid liquid Boiling: liquid gas Sublimation: solid gas

VI. Endothermic & ExothermicB. Exothermic

Heat released (exits the system) Freezing: liquid solid Condensing: gas liquid Deposition: gas solid

Graphic Representations

VII. Phase Diagram A. A graph of the relationship

between all three physical states

Unique to a single substanceOne line for solid-liquidOne line for liquid- gasOne line for solid-gas

B. Points on the Phase Diagram

Triple point: the temperature and pressure at which all three states of a substance are at equilibrium (equal rates of phase change)

Critical point: the temperature and pressure at which the gas and liquid states can coexist at equilibrium

Supercritical fluid: the state where liquid and vapor pressure are indistinguishable (temps above CP)

Entropy vs. Enthalpy ReviewEntropy (S): the disorder

(dispersal of energy and matter) of a system

Enthalpy (H): The amount of heat released or absorbed by a chemical reaction at constant pressure, or heat of reactionAdding heat increases disorder

(entropy)Removing heat decreases disorder

(entropy)

VIII.Latent HeatA.Latent Heat: energy release or

absorbed during a change of state As a solid changes to a liquid(melts),

heat energy must by supplied (externally) to overcome the molecular forces between the particles of the solid

Even though heat is being absorbed during a state change, temperature does not change!!

B.Latent heat of fusion (ΔHfus) Amount of heat required to

convert a specific mass of solid into a liquid without a change in temperature.

C.Latent heat of vaporization (ΔHvap) Amount of heat required to convert

a specific amount of liquid to a gas without a change in temperature

Latent Heat EquationΔQ = m ∙ L

ΔQ = change in heat (transferred)m = massL = latent heat (of fusion or vaporization); replaces ΔT and Cp(specific heat)