PHYSICAL & CHEMICAL CHANGES Objectives: Compare and contrast physical and chemical changes Identify examples of physical and chemical changes

Why do I care? Physical and Chemical changes occur around us everyday! Understanding them will help us better understand our world.

Changes in Matter Change: the act of altering a substance In science, we talk of two types of changes: physical chemical 3

Physical Change Physical change: a change that occurs that does not change the identity or make up of the substance Change in state or phase (Freezing, boiling, melting, sublimating) Changing shape (cutting, folding, twisting, bending) Dissolving 4

Physical Changes Physical changes are changes that alter the size, shape, location or physical state of a substance but not its chemical state. Its still H2O- frozen in snowflakes, as liquid in raindrops, or as a gaseous water vapor, it’s chemical formula has not changed.

Examples A physical change in a substance doesn't change what the substance is. Cutting, folding, or crumpling paper – A physical change in the shape and size of the paper. However, it is still paper! https://www.youtube.com/watch?v=kK4EMUd9eds Dissolving sugar in iced tea- Sugar is still C6H12O6 but now it is spread out in the liquid, it still tastes just as sweet! https://www.youtube.com/watch?v=D1dRdYPRvpY

What Other Kinds of Changes Are Physical? Cutting Tearing Shredding Shrinking Enlarging Change in Phase Relocating Rotating Molding (shaping)

Chemical Changes Chemical change: a change that occurs causing the identity of the substance to change Burning Chemically digesting food (acid and bile) Reacting with other substances A chemical change is also called a chemical reaction 8

Chemical Changes Chemical changes are changes that alter the chemical make up of the substance. New matter is formed with properties that are different than those of the original matter.

Chemical Changes If you end up with a chemical or chemicals that you did not start with. . . It is a chemical change!

Chemical Changes A chemical change is not easily reversed. Difficult to reverse/change back Easy to reverse/change back

Signs That a Chemical Change has occurred Creation of a gas (bubbles) https://www.youtube.com/watch?v=OBdgeJFzSec Creation or loss of heat https://www.youtube.com/watch?v=GQkJI-Nq3Os https://www.youtube.com/watch?v=UMEbeyKrE30 Burning Rotting/molding https://www.youtube.com/watch?v=CcuWuKLoCmU https://www.youtube.com/watch?v=S12zZhdOckc&src_vid=OmcXo9XC6Uc&feature=iv&annotation_id=annotation_14756 Breaking down (decomposition) Precipitation https://www.youtube.com/watch?v=98dbILqPtgI Cooking https://www.youtube.com/watch?v=n6wpNhyreDE Rusting (oxidation)

Heat and light are often evidence of a chemical change.

The strike of a match is a chemical change due to the reaction of the chemicals with oxygen.

Burning wood turns to charcoal and ashes. This is a chemical change.

Is it Physical or Chemical? Change Physical Chemical Melting cheese Burning wood Milk souring Folding up paper Bicycle rusting 16

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