CHANGES OF STATE

 A change of state is the conversion of a substance from one physical form to another.  All changes of state are physical changes.  In a physical change the identity of the substance does not change.

 Five changes of state  freezing  melting  vaporization  Condensation  Sublimation

Which has more energy – gas or liquid? Which has more energy – liquid or solid? Which has more energy – gas or solid?

Energy Changes  Endothermic – energy is absorbed therefore the particles move faster, breaking the bonds  Exothermic – energy is given off therefore particles move slower making them lock into place

Melting  Change from  Change from solid to liquid  Melting points can be used to identify a substance  Melting point is a  Melting point is a characteristic property  The change of energy is endothermic because it absorbs energy thus the particles move away from one another

Freezing  Change from liquid to solid  Molecules must slow to the point where attractions between them overcome their motion  The change of energy is exothermic because energy is removed thereby locking the particles in place

Vaporization  Change from liquid to gas  2 types  evaporation - vaporization that occurs at the surface of a liquid below its boiling point  boiling– vaporization that occurs throughout  boiling– vaporization that occurs throughout a liquid when the temperature is at the boiling point

 Pressure affects boiling point: the greater the pressure, the greater the boiling point  At sea level, water boils at 100 degrees Celsius  The change of energy is endothermic

Condensation  Change from gas to liquid  Particles clump together when the attraction between them overcomes their motion  The change of energy is exothermic because energy is removed  Pressure also affects point of condensation

Sublimation  Change from solid directly to gas  The change of energy is endothermic

Temperature change versus change of state  When temperature changes, the speed of the molecules also changes  While a substance changes a state, its temperature does not change until the change of state is complete