Most people think the visual changes are what really changes the substance, but they forget about the  atoms and the molecules. What really happens in a chemical change is the molecules/atoms interact with another substance and the valance electrons go and take up the empty spaces in the other substance. The chemical change can be big or small, but it doesn’t matter because the two substances still react with each other and cause a chemical change. In a chemical change the signs can vary from color change to temperature change, and you just need to remember what happens to the atoms/molecules is what really matters.