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Chemistry

Physical and chemical change?

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June 25, 2009 2:08PM

Physical change does not change a substance. It could change shape - for example cutting a piece of paper in two is physical change. Putting it through a paper shredder is physical change. When ice melts, that is a physical change. So even if it changes state (solid to liquid, liquid to gas, etc), it is still a physical change. Chemical change is different. The substance has changed in a more substancial way. If you lit the paper on fire it is undergoing a chemical change. There are five basic ways to tell if something is a chemical change, and they are: 1) Heat or light is produced. 2) Bubbles or gas are formed. 3) A precipitate is formed (a small solid is formed within what was just a liquid). 4) It is hard to reverse. 5) A new color is present. So water turning into a gas is a physical change, but if you are boiling it (and bubbles are formed) then it is chemical, and physical (if it changes state).