Chemical changes occur when a substance joins the other to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, can not be reversed except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to allow reactions to occur, called endothermic reactions. Understanding chemical change is a major part of chemistry.
When a chemical reaction occurs, the atoms are reconstituted and the reaction is accompanied by a change in energy when new products are produced. An example of a chemical change is the reaction between sodium and water to produce sodium hydroxide and hydrogen. So much energy is released that hydrogen gas is released spontaneously in the air. This is an example of a chemical change because the final product is chemically different from the substance before the chemical reaction.
Video Chemical change
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Chemists categorize chemical changes into three major classes: inorganic chemical change, organic chemical change and biochemical changes.
Inorganic changes
Inorganic chemistry describes the reaction of elements and compounds that, in general, do not involve carbon. Change usually occurs in the laboratory, or on a larger scale in heavy industry.
Common types of changes include neutralization (acid-base mixing, water and salt generation), oxidation including combustion, redox reactions etc.
Organic changes
Organic chemistry is concerned with carbon chemistry and the reacting elements and compounds. These compounds include mineral oil and all its products and many industrial outputs of pharmaceutical manufacturing, paints, detergents, cosmetics, fuels, etc. Typical examples of organic chemical changes include heavy hydrocarbon cracks in oil refineries to create more gasoline from crude oil, because gasoline has a higher demand than heavier hydrocarbons, such as fuel residuals. Other reactions include, methylation, condensation reaction, polymerization, halogenation etc.
Biochemical changes
Biochemistry deals with the chemical growth and activity of living organisms. It is a chemical in which most of the reactions are controlled by complex proteins called enzymes and are moderated and constrained by hormones. Chemistry is always very complex and still not fully understood. The decomposition of organic matter is also within the scope of biochemistry although in this case is the growth and activity of fungi, bacteria and other micro-organisms involved. Common types of change include all processes involved in photosynthesis, a process in which carbon dioxide and water are converted into sugar and oxygen by plants, the digestion in which the energy-rich substances are used by organisms to grow and move, the Krebs cycle that frees energy from stored reserves, protein synthesis that allows the organism to grow using processes controlled by RNA etc.
Maps Chemical change
Evidence of chemical change
The following may indicate that a chemical change has occurred, although this evidence is not conclusive:
- Odor change.
- Color changes (for example, silver becomes reddish brown when iron is rusty).
- Changes in temperature or energy, such as production (exothermic) or heat (endothermic) loss.
- Composition change - paper to ashes when burned.
- Light and/or heat released.
- The formation of gases, often appearing as bubbles in liquids.
- Formation of precipitate (insoluble particles).
- Decomposition of organic matter (eg, rotting food).
- Changes are difficult or impossible to reverse.
References
Source of the article : Wikipedia
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