Review: Physical and Chemical Changes



Physical ChangeA change (of state or form) in which a new substance is not formed and you can get the original substance easily.Change involving:Melting, boiling, evaporation/condensation,crystallization, dissolvingChemical ChangeA change in which a new substance is formed and you cannot get the original substances back easily.How to recognize a chemical change:A new substance is producedA new odour/taste and/or colour is producedheat or light is producedBubles of gas are formedA precipitate (insoluble solid) is formedUsing the information above, complete the following table:ChangePCWhy?A pie is bakedChocolate meltsA match is litWood is rubbed with sandpaperAn iron bar is heated until its red hotA banana turns brownA day old fish begins to smellA balloon burstsYour hair is cutAshes form when wood is burnedChangePCWhy?Broken glass is crushedWire rustsA firecracker goes BANGA silver spoon tarnishesSugar is dissolved in coffeeMilk turns sourPlace a check in the appropriate column:ChangePhysicalChangeChemicalChangeSalt dissolves in water.yesHydrochloric acid reacts with magnesium to produce hydrogen gas.yesA piece of copper is cut in halfyesA sugar cube is ground up.yesWater is heated and changed to steam.yesIron rusts.yesEthyl alcohol evaporates.yesIce melts.yesMilk sours (goes bad).yesSugar dissolves in water.yesSodium and potassium react violently with water.yesPancakes cook on a griddle.yesGrass grows on a lawn.yesA tire is inflated with air.yesFood is digested in the stomach.yesWater is absorbed by a paper towel.yesEthyl alcohol boils at 79°C.yesPaper burns.yesWater freezes at 0°C.yesChangeFireworks explode.yesAlka-Seltzer gives off carbon dioxide when added to water.yesClouds form in the sky.yesNow your knowledge of the two types of changes will be put to the test! Classify the changes listed below as either physical or chemical, and then give a reason for your decision. The first one has been done for you!ChangeTypeReasonA newspaper yellowed after a few weeksChemicalColour change is permanentThe steel wool turned the black pot a shiny silvery colourPhysicalSteel wool removed burnt food from pot. No new substances formed in the processAcid caused limestone to fizzChemicalThe fizzing is carbon dioxide gas that forms when the acid reacts with the calcium carbonate that makes up the limestoneThe back steps are rotting outChemicalMicroorganisms, insects and worms are digesting the wood breaking cellulose into simpler compounds. There is a change in colour and odour.Spilled gasoline dried but left a bad odour in the roomPhysicalState changes like evaporation are physical changesThe gravy in the refrigerator jelledChemicalThe strands of protein reacted with one another forming cross-linking that holds them together to make a solid. If you heat the gravy, the bonds break and the gravy become a liquidSee: meat turned brown as it cookedChemicalChange in colour, odour and taste.You got a cavity in your toothChemicalThe rotted part of the tooth is a new substance. Acid produced by bacteria digesting sugar results in a chemical reaction between acid and tooth enamelThe paint on your car turned dullPhysicalNo new substance is formed. The paint wears out over time. ................
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