Decomposition, the opposite of combination, involves the breakdown of a single substance into two or more different substances. The signs ofchemical changeincludechangesin color, temperature, the production of light,changesin odor, and the formation of gases.

A chemical change, also known as achemical reaction, is a process where one or more substances are altered into one or more new and different substances. In other words, a chemical change is a chemical reaction involving the rearrangement of atoms. While a physical change can often be reversed, a chemically change typically cannot be, except through more chemical reactions. When a chemical change occurs, there is also a change in the energy of the system. A chemical change that gives off heat is calledan exothermic reaction.

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during a chemical change following changes occur : 1. change in state 2. change in colour3. change in odour / smell4. change in temperature

Physical Change or Chemical Change?

One way to think about physical changes is that they are reversible since they do not affect a substance’s chemical identity. These include changes in size, shape, texture or state. A good example of physical change is ice melting into water. This change of state is a physical change since scooping up the water and returning it to the freezer reverses it. Chemical changes, on the other hand, can’t reverse since they involve breaking bonds between molecules and forming new bonds.

Changes in Temperature

While you can heat any substance, the spontaneous release of heat after mixing compounds together is a good indicator that a chemical reaction has taken place. Reactions that release heat are also called exothermic reactions. An example of a chemical change that releases heat is the thermite reaction, which is what causes fireworks to explode.