Sunday, August 2, 2009

Examples of chemical changes and physical changes

Chemical changes are happening all the time. There are several different types of chemical change, including: synthesis, decomposition, single displacement, double displacement, neutralization, precipitation, combustion, redox and wood burning.
A primary example of a chemical change is the combustion of methane to produce carbon dioxide and water.

• iron rusting (iron oxide forms)
• gasoline burning (water vapor and carbon dioxide form)
• eggs cooking (fluid protein molecules uncoil and crosslink to form a network)
• bread rising (yeast converts carbohydrates into carbon dioxide gas)
• milk souring (sour-tasting lactic acid is produced)
• suntanning (vitamin D and melanin is produced)

Physical change rearranges molecules but doesn't affect their internal structures. Some examples of physical change are:
• whipping egg whites (air is forced into the fluid, but no new substance is produced)
• magnetizing a compass needle (there is realignment of groups ("domains") of iron atoms, but no real change within the iron atoms themselves).
• boiling water (water molecules are forced away from each other when the liquid changes to vapor, but the molecules are still H2O.)
• dissolving sugar in water (sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.)
• dicing potatoes (cutting usually separates molecules without changing them.)

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