What are the five "clues" that a chemical change has occurred?
Change in colour, change in temperature, change in smell, formation of a precipitate, formation of gas bubbles
A chemical change occurs when the reactants chemical compositions have changed e.g. chemical bonds have been broken and formed. A chemical change can be indicated by a change in colour, change in temperature (exothermic or endothermic), change in smell, formation of a precipitate, or the formation of gas bubbles.
Note: the five "clues" are not definite indicators, a chemical change may not always be occurring e.g. if you paint a wall it has changed colour, but the actual composition hasn't changed. It is a physical change, not a chemical change.