The concept chemical reaction or chemical change can be defined as the set of processes with which a change in the nature of a substance takes place. Some examples of these types of chemical reaction can be found through combustion and corrosion .
When a chemical reaction takes place
Chemical reactions are not always easy to detect, but it is certain that there are a series of signs that allow their identification. Among these signs, we can highlight the following: change in color (an unmistakable sign of the appearance of several substances other than the initial ones), absorption or release of heat (through the change in temperature ), gas release (the chemical reaction materializes in the form of a new substance in gaseous state ) or the appearance of precipitate or sediment (some of these new substances are insoluble).
Along with all this, we can add other changes that are less common or more difficult to detect, such as changes in odor or acidity, as well as the emergence of new magnetic, electrical or optical properties.
Physical or chemical change
Chemical reactions are present everywhere even though we are often not aware of what is happening. Just pay a little attention to find countless transformations in the matter around us. However, not all of these changes in matter are the result of a chemical change or reaction.
These chemical reactions establish a transformation that directly affects the nature of matter, but when this change is only on the surface, as in a change of shape, it means that we are facing the presence of a physical change.
Taking both definitions into account, we can be clear that the problem to differentiate both physical and chemical reactions lies in the fact of understanding how the change in the nature of matter happens.
According to Lavoisier’s law, matter cannot disappear unless a new substance arises from the atoms of the previous one.
Therefore, the simplest way to differentiate physical from chemical reactions is to see whether with the change in matter new substances arise or any of the previously existing ones disappear. If the answer is yes, we are facing a chemical reaction, while if the result of this transformation has no changes in the substances that make up matter, then it is a physical reaction.