Physical changes are reversible while chemical changes are not.


Both physical changes and chemical changes are reversible. Not all reactions are reversed easily, but it may occur.

Why the misconception:

Often the differences between chemical and physical changes are taught incorrectly. Teachers want to make a clear distinction between chemical an physical changes so it is often taught that physical changes are reversible while chemical changes are not. Consider the example of the Utah Standards. In 5th grade in standard 1 objective 3d reads: compare a physical change to a chemical change. Whereas in comparison, 8th grade standard 1 objective 2a is: identify observable evidence of a physical change (e.g. change in shape, size, phase). Also in 8th grade standard 1 objective 2b is: identify observable evidence of a chemical change (e.g. color change, heat or light given off, change in odor, gas given off). For 5th grade teachers the standard does not remind them what classifies a physical and chemical change, but in the 8th grade it is more clearly classified for the teacher. Also, if the teacher was taught the misconception then the misconception will be passed down to their students.

Easy demonstration:

Most students understand how physical changes are reversible, but often students do not observe a simple reversed chemical reaction. An easy demonstration to show a reversible chemical change is the blue bottle demonstration. For this demonstration KOH is dissolved in water and then dextrose is dissolved in the solution and the indicator methylene blue is added. When then indicator is added to the solution it causes the solution to turn blue. Over time the blue color fades and the solution becomes colorless, but if the flask is shaken then the blue color will reappear.

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