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From Wikipedia

Chemical change

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.

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:

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

From Yahoo Answers

Question:10 points for the best answer

Answers:Select anything from an entry-level chemistry book/web site! Cooking Respiration (O2 to CO2) Burning fuel (or anything else) Synthesis of proteins by the body Photosynthesis Depleting a battery Concrete setting etc..

Question:I combined Hydrochloric Acid and Bromothymol Blue in a lab, and observed it created a yellow solution. Was the colour change be a result of a chemical reaction, or not?

Answers:No, that was a physical change. A chemical change is when it gives off light, heat, gas, bubbles, precipitate, etc.

Question:Give an example of a chemical change that does not show an obvious energy change. How do you know a change occurs?

Answers:examples of chemical change: 1.fruits taste sweeter when ripe 2.wood becomes ash when burned 3.browning of peeled banana 4.coconut water turned into vinegar You may know if it undergoes chemical change due to signs of chemical change: 1.evolution of light and heat 2.evolution of gas 3.formation of a precipitate 4.production of mechanical energy 5.production of electrical energy

Question:Give an example where a change of color indicates a physical change and not a chemical change.

Answers:Dilute a concentrated colored solution. For instance, if you start out with a dark red solution and you dilute it enough, the color will become orange. Then, if you dilute it further it will become yellow or faint pink.

From Youtube

Examples of Chemical and Physical Changes :Caila & Tina