A chemical change occurs when components have been mixed together and cannot be separated back to their original state. For an example, trail mix is NOT a chemical change because you can seperate the almonds from the raisons. However, a pancake is an example of a chemical change because you cannot seperate the flour, vanilla, and egg back to their original states. :)
A chemical change is typically an irretrievable chemical reaction relating to the reorganization of the atoms of one or more substances and a change in their chemical properties or composition, which result to the formation of at least one new substance. A common example of a chemical change is the formation of rust on iron. In other words this is a rearrangement of the atomic array of matter which results in a change of physical properties.