Is the process by which the substance changes from solid to liquid. Phase Change: Is a change from one state (solid or liquid or gas) to another without a change in chemical composition. Heat Example: H2O (s) H2O (l) Melting: Is the process by which the substance changes from solid to liquid. The temperature at which this process occurs is called melting point. Melting point (H2O) = 0oC

Is the process by which the substance changes from liquid to solid. - Heat H2O (l) H2O (s) Freezing: Is the process by which the substance changes from liquid to solid. The temperature at which this process occurs is called freezing point. Freezing point (H2O) = 0oC Melting point = Freezing point Solid Liquid Melting Freezing

Is the process by which the substance changes from liquid to gas. Heat H2O (l) H2O (g) Boiling: Is the process by which the substance changes from liquid to gas. The temperature at which this process occurs is called boiling point. Boiling point (H2O) = 100oC Condensation: Is the process by which the substance changes from gas to liquid.

Boiling point = Condensation point Liquid Gas Boiling Condensation Boiling point = Condensation point Ex: For water both are100oC. (Liquid water boils at 100oC and steam condenses at 100oC).

Is the process by which the substance changes from solid to gas. Phase Changes: Sublimation: Is the process by which the substance changes from solid to gas. Deposition: Is the process by which the substance changes from gas to solid.

Sublimation point = Deposition point Solid Gas Sublimation Deposition Sublimation point = Deposition point Ex: For CO2 both are-78oC. (Solid CO2 sublimes at -78oC and gas CO2 deposits at -78oC).

Melting Boiling Sublimation Phase Changes: Melting Boiling Sublimation Absorb energy (endothermic processes) Freezing Condensation Deposition Release energy (exothermic processes)

Gas Liquid Solid Sublimation Condensation Deposition Vaporization Melting Solid Liquid Freezing

Heating Curve of Water: A – B ----- Kinetic (Temperature increases) Thermal Energy Is converted into Temperature B – C ----- Potential (Temp. doesn’t change) Phase change C – D ----- Kinetic D – E ----- Potential (Temp. doesn’t change) E – F ----- Kinetic F Vapor Boiling Point Vaporization (Boiling) D E 100 - - - - - - - - - - - - - - - - - - - - - - - - Liquid Melting Point Liquid & Vapor 0 - - - - - - - - - - - - B Melting C Solid & Liquid Solid A 20 100 200 740 Heat Added (kcal)

Vaporization Boiling Evaporation The conversion occurs in the entire mass of a liquid, this process require more thermal energy than evaporation. When the conversion occurs at the surface of a liquid at room temperature.

evaporation is a cooling process. As evaporation occurs, the particles with the highest kinetic energy tend to escape first. As evaporation takes place, the liquid’s temperature decreases because the particles take the energy from its surrounding to become to gas, then evaporation is a cooling process.

You can observe the effects of evaporative cooling on hot days. When you perspire, water molecules in your perspiration absorb heat from your body and evaporate from the skin’s surface. This evaporation leaves the remaining perspiration cooler. * The perspiration that remains cools you further by absorbing more body heat.