CHANGES OF STATE ARE PHYSICAL CHANGES Section 2.2 CHANGES OF STATE ARE PHYSICAL CHANGES

II. Solids can become liquids, and liquids can become solids Examples of solids that can change to liquids Ice melts into water Others???

A. Melting Melting is the process of a solid becoming a liquid Different solids melt at different temperatures Energy is GAINED making the particles move FASTER Melting point is the lowest temperature at which a substance melts Substances with a well-defined melting point have an orderly structure

B. Freezing Freezing is the process of a liquid becoming a solid many substances are “frozen” at room temperature Energy is LOST making the particles move SLOWER Freezing point is the temp. at which a liquid becomes a solid Freezing point of a substance equals the melting point of that same substance

A. Evaporation Evaporation is the process of a liquid becoming a gas Usually occurs at the surface Solids can lose particles at the surface, similar to liquids, by the process of sublimation Energy is GAINED making the particles move FASTER

B. Boiling Boiling is the process of changing a liquid to a gas by producing bubbles which contain dissolved air Can occur only when a certain temp. has been reached which is called the boiling point The boiling point of water at higher elevations is lower because of lower air pressure

B. Boiling (continued) Different substances have different boiling points a) Helium boils at -270°C (-454°F) b) Aluminum boils at 2519°C (4566°F) Energy is GAINED making the particles move FASTER

C. Condensation Condensation is process by which a gas becomes a liquid Energy is LOST making the particles move SLOWER Like evaporation, condensation occurs over a wide range of temperatures