ⓘ Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into ..


ⓘ Chemical change

Chemical changes occur when a substance combines with another 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, are not reversible except by further chemical reactions. Some reactions produce heat and are called exothermic reactions and others may require heat to enable the reaction to occur, which are called endothermic reactions. Understanding chemical changes is a major part of the science of chemistry.

When 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 and water to produce sodium hydroxide and hydrogen. So much energy is released that the hydrogen gas released spontaneously burns in the air. This is an example of a chemical change because the end products are chemically different from the substances before the chemical reaction.


1.1. Types Inorganic changes

Inorganic chemistry describes the reactions of elements and compounds that, in general, do not involve carbon. The changes typically take place in laboratories, or on a larger scale in heavy industries.

Typical types of change include neutralization mixing an acid with a base, resulting in water and salt, oxidization including combustion, redox reactions etc.


1.2. Types Organic changes

Organic chemistry is concerned with the chemistry of carbon and the elements and compound with which it reacts. These compounds include mineral oil and all of its products and much of the output of industries manufacturing pharmaceuticals, paints, detergents, cosmetics, fuels etc. Typical examples of organic chemical changes include cracking heavy hydrocarbons at an oil refinery to create more gasoline from crude oil, as gasoline is in higher demand than the heavier hydrocarbons, such as residual fuel oils. Other reactions include, methylation, condensation reactions, polymerisation, halogenation etc.


1.3. Types Biochemical change

Biochemistry deals with the chemistry of the growth and activity of living organisms. It is a chemistry where most reactions are controlled by complex proteins called enzymes and are moderated and limited by hormones. The chemistry is always highly complex and is still not fully understood. Decomposition of organic material is also within the scope of biochemistry although in this case it is the growth and activity of fungi, bacteria and other micro-organisms that is involved. Typical types of change include the processes involved in photosynthesis, a process in which carbon dioxide and water are changed into sugars and oxygen by plants, digestion in which energy rich materials are used by organisms to grow and move, the Krebs cycle which liberates energy from stored reserves, protein synthesis which enables organisms to grow using processes controlled by RNA, etc.


2. Evidence of a chemical change

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

  • Formation of a precipitate insoluble particles.
  • Change of color for example, silver to reddish-brown when iron rusts.
  • The decomposition of organic matter for example, rotting food.
  • Formation of gases, often appearing as bubbles in liquids.
  • Change of odor.
  • Light and/or heat given off.
  • Change in temperature or energy, such as the production exothermic or loss endothermic of heat.
  • The change is difficult or impossible to reverse.
  • Change of composition - paper turning to ash when burned.
  • quality that can be established only by changing a substance s chemical identity. Simply speaking, chemical properties cannot be determined just by viewing
  • encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei
  • Chemical thermodynamics is the study of the interrelation of heat and work with chemical reactions or with physical changes of state within the confines
  • Physical changes are changes affecting the form of a chemical substance, but not its chemical composition. Physical changes are used to separate mixtures
  • Chemical kinetics, also known as reaction kinetics, is the branch of physical chemistry that is concerned with understanding the rates of chemical reactions
  • liquids, gases, or plasma, and may change between these phases of matter with changes in temperature or pressure. Chemical substances may be combined or converted
  • In thermodynamics, chemical potential of a species is energy that can be absorbed or released due to a change of the particle number of the given species
  • objective of a chemical plant is to create new material wealth via the chemical or biological transformation and or separation of materials. Chemical plants use
  • final temperatures are the same. This change in energy can be estimated from the bond energies of the various chemical bonds in the reactants and products
  • U.S. Chemical Warfare Service CWS during World War I. Its name was changed to the Chemical Corps in 1946. For most of its history, the Chemical Corps