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

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Presentation on theme: "Foundations of Chemistry Matter Chapter 7 Lesson 3 Physical Changes Mr. Nigh Science 7."— Presentation transcript:

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

2 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

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

4 Physical changes of wool 1.Wool is sheared from sheep 2.Wool fibers are spun into yarn 3.The yarn is dyed a special color. 4.The yarn is knitted into a jacket.

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

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

7 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.

8 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

9 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

10 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

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

12 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)

13 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.

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

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

16 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


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