- Slides: 14
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=c. Vydmlz 0 F-E Halloween Clock Reaction https: //www. youtube. com/watch? v=Tv 6_Isdna. Gg Sugar and Sulfuric Acid https: //www. youtube. com/watch? v=AP 6 r. TJi 59 NM 6 Chemical Reactions that Changed the World PBS https: //www. youtube. com/watch? v=jb 4 CMn. T 2 -ao