Is a process in which reactants are changed into one or more different products. A chemical change occurs whenever compounds are formed or decomposed. During this reaction, there is a rearrangement of atoms that makes or breaks chemical bonds. This change is usually not reversible, unlike physical changes, which typically are reversible. In short, chemical change is a change of one substance into another substance (i.e. a new substance is formed). By contrast, no new substance is formed in a physical change (for example, the melting of ice is a physical change because when ice changes into water, no new substance is formed.)
In a chemical reaction, bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another. Some exothermic reactions may be hot enough to cause certain chemicals to also undergo a change in state; for example in the case of aqueous solutions, bubbles may not necessarily be newly produced gas but instead water vapor.
Chemical changes are happening very often. When wood burns it is a chemical change. There are several different types of chemical change. These include synthesis, decomposition, single displacement, double displacement, neutralization, precipitation and redox.
Other examples of chemical changes are:
The following can indicate that a chemical change took place, although this evidence is not conclusive: