In a chemical change, bonds are broken and new bonds are formed between different atoms. This breaking and forming of bonds takes place when particles of the original materials collide with one another. Some exothermic reactions may be hot enough to 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 vapor.

Whenever chemical reactions occur, the atoms are rearranged and the reaction is accompanied by an energy change as new products are generated. An example of a chemical change is the reaction between sodium hydroxide and hydrogen chloride to produce sodium chloride, or table salt. This reaction is so exothermic, meaning it releases heat in the form of energy, that even flames are generated. This is an example of a chemical change because the end product is molecularly different from the starting molecules.^[1]

Chemical changes are happening all the time. There are several different types of chemical change, including: synthesis, decomposition, single displacement, double displacement, neutralization, precipitation, combustion and redox.

Examples of chemical changes

A primary example of chemical change is the combustion of methane to produce carbon dioxide and water.

Other examples of chemical changes are:

• Decomposition
• Neutralization (Mixing an acid with a base, resulting in water and a salt).
• Photosynthesis - a process in which carbon dioxide and water are changed into sugars by plants.
• Cracking heavy hydrocarbons to create lighter hydrocarbons (part of the process of refining oil).
• Cooking examples: cake, pancakes, and eggs/bacon
• Oxidation examples: rust or tarnishing
• Ripening examples: bananas, tomatoes or potatoes

Evidence of a chemical change

The following can indicate that a chemical change took place, although this evidence is not conclusive:

• Change of odor
• Change of color (for example, silver to reddish-brown when iron rusts).
• Change in temperature or energy, such as the production (exothermic) or loss (endothermic) of heat.
• Change of form (for example, burning paper).
• Light, heat, or sound is given off.
• Formation of gases, often appearing as bubbles.
• Formation of precipitate (insoluble particles).
• The decomposition of organic matter (for example, rotting food).

A chemical change can have a huge impact on a physical change.

Laws of chemical changes

Chemical law

References

1. ^ Carpi, Anthony, Ph.D. “Chemical Reactions.” Vision Learning. Vision Learning Inc. , 2009. Web. 6 Oct. 2009.

A chemical change (chemical reaction) is a change of materials into other, new materials with different properties, and one or more new substances are formed. Burning of wood is a chemical change as new substances which cannot be changed back (e.g. carbon dioxide, water vapor) are formed. For example, if wood is burned in a fire place, there is not wood anymore but ash. Other examples include burning of a candle, rusting of iron, 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.