How do you identify whether a reaction was a physical or chemical change? What properties and indicators can help you classify between the two? Read to find out!
In chemistry, reactions can be classified as either a physical or chemical change. Although classifying the differences between them can be tricky, there are some signs you can look out for that can help you!
First of all, what exactly defines each of these reactions? Chemical reactions are processes in which the composition of the substances change as they react with each other. Physical reactions, in fact, are not actual "reactions", as no changes actually occur in the composition of the reactants. The more accurate term for them is physical "changes" since only the physical properties of the substances change, and the chemical properties remain consistent.
Indicators of Physical Reactions
When physical reactions occur, the substance that undergoes the change still has the same chemical makeup. By the end of the "reaction", it will still be identified with the same chemical name. For instance, ice can undergo a physical change to water, and its chemical makeup will still be H2O after the change. Some common physical changes in substances include changes in texture, state of matter (solid, liquid, gas), shape, and viscosity (consistency or thickness). These changes only affect a substance's physical properties and not its actual chemical composition.
Indicators of Chemical Reactions
On the other hand, chemical reactions involve the breaking and formation of bonds, which gives the substances a different chemical makeup and formula. Some signs that indicate a chemical change can include odor, precipitate formation (a solid inside a solution), and bubble formation. If the substance you end up with has entirely different properties and has changed into a completely new substance, you can classify it as a chemical change.
Overlapping Indicators
However, some indicators, such as a change in temperature and change in color, can be seen in both physical and chemical changes. To tell them apart, you must look at how the change occurred.
For temperature, if a substance is heated, such as water on a stove, then it is a physical change since the water vapor formed is still the same substance as the water, H2O. If the temperature occurred from the substances themselves without external conditions, then it is a chemical change, such as fireworks that produce heat after the substances react.
For color, things such as mixing two different colored substances together or painting a substance is not a result of any change in chemical makeup, and are just physical changes. However, things such as metal rusting are chemical changes, since the changes in color are results of the metal substance itself forming new bonds with the compounds in the air.
Thank you for reading, and have fun experimenting!
Reference:
Libretexts. “Chemical Change vs. Physical Change.” Chemistry LibreTexts, 22 Aug. 2020, chem.libretexts.org/Bookshelves/Physical_and_Theoretical_Chemistry_Textbook_Maps/Supplemental_Modules_(Physical_and_Theoretical_Chemistry)/Fundamentals/Chemical_Change_vs._Physical_Change.
My wife was diagnosed of Parkinsons Disease at age 59. She had slurred speech and severe tremors, she was put on sinemet and Siferol for over 14 months. During this time span she was also diagnosed with dementia. Her care provider adivce we start on herbal treatment from ULTIMATE HERBAL CLINIC (Reach them at www.ultimateherbalclinic.com). Within 2 months on the treatment she improved dramatically. At the end of the full treatment course, the disease is totally under control, no case of hallucination, tremors, weakness, muscle pain and she can walk just fine