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#REDIRECT [[Chemical reaction]] {{R from merge}}
The following is a list of evidence that ''can'' indicate that a chemical change took place. Note that this evidence is not exclusive. For example, placing a pot of water on a hot stove element causes a change in temperature and a gas to be released (water vapour) but a chemical change did not take place.
* the formation of [[gas]]
* change in colour (e.g., rusting of iron causes a change in colour from silver to reddish-brown)
* change in temperature or energy, such as the production (exothermic) or loss (endothermic) of [[heat]]
* production of [[light]], whether visible or invisible
* the appearance of a new [[substance]]
* a change in amount of a starting [[substance]]
* blabla
*Examples: baking a cake, a rusty nail, fireworks, vitamins changing color in sunlight, a candle burning, an egg being fried, etc.
When new substances are formed, a chemical change has occurred, and a [[chemical reaction]] has taken place. Note that, in a few cases, exothermic reactions may be hot enough 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 vapour.
There is very little about a chemical change that can distinguish it from a [[physical change]], and distinguishing between the two is often difficult for an introductory student. For example, a [[nuclear explosion]] is an example of a physical change that contains many of the above events (changing from one substance to another, release of light and heat, and possibly formation of a gas). For a change to be considered a chemical change, [[chemical bonds]] must be altered in some way.
==External links==
* http://antoine.frostburg.edu/chem/senese/101/reactions/slides/index.shtml
[[Category:chemistry]]
[[simple:Chemical change]]
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