Chemical change

Burning wood is an example of a chemical change that is not reversible

A chemical change (chemical reaction) is a change of materials into other materials with different properties.

Chemical changes occur when a substance combines with another to form a new substance, or, chemical decomposition into two or more different substances. These processes are called chemical reactions.

Burning of wood is a chemical change as new substances which cannot be changed back (e.g. carbon dioxide) are formed. For example, if wood is burned in a fireplace, there is not wood anymore but ash. Other examples include burning of a candle, rusting of iron, baking a cake, etc. Special details that describe how a chemical change takes place are called chemical properties.

Compare: physical change. The opposite of a chemical change is a physical change. Physical changes are a change in which no new substances are formed, and the substance which is changed is the same. For instance, if a stick of wood is broken, there is still a stick of wood; it is just broken.

More examples include changes of shape, changes of states, passing electricity through a copper wire, breaking of wood, shattering of glass, pouring of water, etc. Special details which do not change in a substance without new substances being formed are called physical properties.

Chemical Change Media

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  A thermite reaction using iron(III) oxide. The sparks flying outwards are globules of molten iron trailing smoke in their wake.

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  Antoine Lavoisier developed the theory of combustion as a chemical reaction with oxygen.

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  As seen from the equation CH
  4 + 2O
  2 → CO
  2 + 2 H
  2O, a coefficient of 2 must be placed before the oxygen gas on the reactants side and before the water on the products side in order for, as per the law of conservation of mass, the quantity of each element does not change during the reaction.

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  An example of organic reaction: oxidation of ketones to esters with a peroxycarboxylic acid

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  Isomerization of azobenzene, induced by light (hν) or heat (Δ)

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  Representation of four basic chemical reactions types: synthesis, decomposition, single replacement and double replacement.

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  Illustration of a redox reaction

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  Sodium chloride is formed through the redox reaction of sodium metal and chlorine gas

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  Ferrocene – an iron atom sandwiched between two C5H5 ligands

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  Diagram showing the differences between a compound, a precipitate, a supernate, and a suspension.