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Physical vs Chemical Changes & Observing Chemical Reactions


This week in Science 6, students analyzed the difference between physical and chemical changes, learned how to read chemical equations, and started preparing to create and observe a chemical reaction.  Students discovered that physical changes are a change in physical state (solid to liquid to gas, etc) or in appearance, and chemical changes happen on a molecular level when you have two or more molecules that interact.  Chemical changes happen when atomic bonds are broken or created during chemical reactions.

physical vs chemical change

Melting a sugar cube is a physical change because the substance is still sugar.  Burning a sugar cube is a chemical change.  Fire activates a chemical reaction between sugar and oxygen.  The oxygen in the air reacts with the sugar and the chemical bonds are broken.

Iron (Fe) rusts when it is exposed to oxygen gas in the air.  You can watch the process happen over a long period of time.  The molecules change their structure as the iron is oxidized, eventually becoming iron oxide (Fe2O3).  Rusty pipes in abandoned buildings are real world examples of the oxidation process and we just saw some during our Mass MoCA field trip this week.

Next week students will create and observe a chemical reaction between baking soda and vinegar, and be able to explain the reaction on the molecular level.  Here is a key to reading chemical formulas:

chemical formula

And here are the parts of a chemical equation:

parts of a chemical equation

And finally, here is the new vocabulary we studied this week:

chemical change: a change that results in the formation of one or more new substances: chemical reaction.
reactant: the starting substances in a chemical reaction, written before the arrow.
product: the end result(s) in a chemical reaction; written after the arrow.
closed system: a container (system) that does not allow atoms in or out (closed); mass is conserved (stays the same).
open system: atoms can move in and/or out of the system; mass is not conserved (it changes).
endothermic reaction: absorbs heat energy; will feel cold because it takes heat away from your hand.
exothermic reaction: gives off heat energy; will feel warm because it gives heat to your hand.

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