Physical vs. Chemical Changes

Physical Change A change that does not create a new substance Most are easy to reverse

Examples bending (nail) crushing (can) cutting (paper) dissolving (sugar) freezing (ice) melting (butter) molding (clay) pounding (metal) mixing (kool-aid) sanding (wood)

Chemical Changes A change that creates new substances with different properties Hard to reverse

Evidence of chemical changes A new substance is formed Change in odor (sour milk) Change in color (jewelry, copper dome) Production of heat (exothermic) (hand warmer) Absorption of heat (endothermic) (cool pack) Fizzing, foaming, bubbles (release of gas) (effervescent tablets) Release of sound or light (fireworks) Forms a precipitate (a solid from solutions)

Chemical Reaction Sugar and Sulfuric Acid: Before and After!

Comparing Physical and Chemical Changes Remember—Always ask yourself…did the composition (what makes up the material) change? If it did, a chemical reaction occurred. If it didn’t, a physical reaction occurred.

Let’s Practice—Decide whether each change is physical or chemical Melting chocolate Baking a cake Burning a match Adding kool-aid mix to water Crushing a pill Evaporating water Digesting food Making Jello Burning gas in a car 

Using a cookie cutter to cut cookie dough Baking cookies The Statue of Liberty oxidizing Molding play-dough Leaves changing color in the fall Metal rusting Silver tarnishing Turning water into ice Cracking an egg A battery working Frying an egg

Cool Chemical Reactions Gummy Bear Reaction https://www.youtube.com/watch?v=cVydmlz0F-E Halloween Clock Reaction https://www.youtube.com/watch?v=Tv6_IsdnaGg Sugar and Sulfuric Acid https://www.youtube.com/watch?v=AP6rTJi59NM 6 Chemical Reactions that Changed the World PBS https://www.youtube.com/watch?v=jb4CMnT2-ao