Foundations of Chemistry Matter Chapter 7 Lesson 3 Physical Changes Mr. Nigh Science 7

Physical Changes A Physical change is a change in any physical property of a substance, not in the substance itself. Stretching a rubber band is a physical change. Changing the state of matter of a substance (water to ice) is a physical change 2

A square of clay that has been molded may have different physical properties such as shape and volume, but it is still clay.

Physical changes of wool Wool is sheared from sheep Wool fibers are spun into yarn The yarn is dyed a special color. The yarn is knitted into a jacket. 4

The wool has gone through many physical changes, but is still the same substance

Adding Thermal Energy When Thermal energy is added to a substance, the particles move faster and faster. Substances may change their state of matter

REMEMBER: particles are always in motion, even in solids REMEMBER: particles are always in motion, even in solids. Because the particles in a solid are bound together, they do not move from place to place-they vibrate As a solid heats up, the particles vibrate faster until they break loose and slide past each other-in other words turn into a liquid. 7

Evaporation is the process by which a liquid becomes a gas It usually occurs at the surface of a liquid The fastest moving particles at the surface can break away from the liquid and escape to become gas particles 8

Sublimation Under certain conditions, solids can lose particles through a process similar to evaporation. When solids change directly to a gas, it is known as sublimation. Dry ice or frozen carbon dioxide sublimates in normal atmospheric conditions 9

Removing Thermal Energy When thermal energy is removed from a gas, such as water vapor, particles in the gas move more slowly and the temperature decreases

Condensation is the process by which a gas changes its state to become a liquid When you cool a gas it loses energy. As the particles move more slowly, the attractions among them cause water droplets to form 11

Freezing is the process by which a liquid becomes a solid A frozen substance does not have to have an extremely cold temperature, some substances are frozen at room temperatures (ie. candles, pop cans) 12

The freezing point of a substance is the same as the melting point The temperature at which a specific liquid becomes a solid is its freezing point. The freezing point of a substance is the same as the melting point At temperatures below this point the substance is a solid, above this point the substance is a liquid. 13

Deposition Deposition is the change from a gas directly into a solid

Dissolving If you add salt to a beaker of water and it disappears, the substance is dissolving

Conservation of Mass The particles of matter that are present before a physical change are the same as those present after a physical change Thus, the total mass before and after physical change is identical