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

I.Freezing and Melting A. Freezing: change from liquid to solid Freezing 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 Condensation A. Evaporation: change from liquid to gas Boiling point: the temperature at which a liquid changes into gas B. Condensation: change from gas to liquid

III.Deposition and Sublimation A. Sublimation: change from solid to gas The thin film of ice on the windshield going away B. Deposition: change from gas to solid Frost on the grass

IV.Energy in State Changes A. The energy of rapid random motion of atom sized particles 1.All matter has energy related to this 2.Energy increases and temperature increases As energy is added the particles move more rapidly The more rapid the movement the state can be overcome

V.Temperature A. 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 & Exothermic A. Endothermic Heat required (enters the system) Melting: solid  liquid Boiling: liquid  gas Sublimation: solid  gas

VI.Endothermic & Exothermic B. 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 substance One line for solid-liquid One line for liquid- gas One 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 Review Entropy (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 reaction Adding heat increases disorder (entropy) Removing heat decreases disorder (entropy)

VIII.Latent Heat A. 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 (ΔH fus ) Amount of heat required to convert a specific mass of solid into a liquid without a change in temperature. C. Latent heat of vaporization (ΔH vap ) Amount of heat required to convert a specific amount of liquid to a gas without a change in temperature

Latent Heat Equation ΔQ = m ∙ L ΔQ = change in heat (transferred) m = mass L = latent heat (of fusion or vaporization); replaces ΔT and C p (specific heat)