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In the last week and a half we learned differences between physical and chemical changes.  We performed experiments where we either burned a substance or combined two substances together.  From what I saw in our experiments I would say that chemical changes occur when a new substance is produced and physical changes occur when the substance stays the same and there is no molecular change to the substance.  Some properties of a chemical change would be a new substance is produced, heat is produced, or there is a color change.  An example of a chemical change from our lab was when we put the piece of magnesium metal into a flame and light and heat were produced.  Afterwards the magnesium had turned into a difference ash like substance.  An example of a physical change from our lab is when we put the wire test rod into a flame.  The wire did get red hot but it stayed the same substance meaning it was a physical change.  We also learned about mass of substances when they are burned or combined with other substances.  If the mass of two substances stayed the same when they were combined then there was no interaction between them and it was just a mixture.  When we performed the experiment where measured the mass of steel wool, burnt it, then measured again the mass became greater because more air was added to it.  When we did the experiment where we just pulled the steel wool apart the mass decreased very little.