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How do you distinguish between physical changes and chemical changes? What is the difference?

Éveline O

Thank you for your question!

First, physical changes are a type of change that do not alter the nature or the characteristic properties of matter. When the physical change is completed, the substances are still of the same kind.

Secondly, a chemical change is a change that modifies the nature and characteristic properties of matter. New substances are formed at the end of the change.

Distinguishing the two types of changes often comes down to correctly identifying the signs of their presence.

Physical changes give the following clues to their presence:

• Changes in the shape of an object: deformation, torsion, stretching, breaking, tension, etc.

• Changes in the state of an object: transitions between states of matter (condensation, boiling, sublimation, etc.)

• Preparation and separation of mixtures: preparation and separation of mixtures only changes the properties physical objects by changing their arrangement in space

Often, chemical changes give the following clues to their presence:

• Gaseous emissions (effervescence): the production of a gas which was not present at the start of the reaction

• Heat absorption or generation: increase or decrease in the temperature of the immediate environment of the reaction

• Emission of bright light

• Significant change of color by the reactants of a reaction: significant change and not small (such as the change of color after dilution)

• Precipitate formation: an insoluble solid formed by liquid substances that react together

All in all, the best way to distinguish physical changes from chemical changes and vice versa is to refer oneself to the definition of both phenomena. One has to determine whether or not a transformation changes the nature and characteristic properties of a substance.

Don’t hesitate to ask other questions!