Chemical change - wikipedia Chemical change hide This article has multiple issues. Please help improve it or discuss these issues on the talk page. ( Learn how and when to remove these template messages ) This article does not cite any sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( September 2014 ) This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( January 2010 ) 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. Contents 1 Types 1.1 Inorganic changes 1.2 Organic changes 1.3 Biochemical change 2 Evidence of a chemical change 3 References Types Chemists categorize chemical changes into three main classes : inorganic chemical changes, organic chemical changes and biochemical changes. 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. 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. 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 all the process 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, Krebs cycle which liberates energy from stored reserves, protein synthesis which enable organisms to grow using processes controlled by RNA etc. Evidence of a chemical change The following can indicate that a chemical change has taken 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 composition - paper turning to ash when burned. Light and / or heat given off. Formation of gases, often appearing as bubbles in liquids. Formation of a precipitate ( insoluble particles ). The decomposition of organic matter ( for example, rotting food ). The change is difficult or impossible to reverse. References Chemical bonds Intramolecular ( strong ) Covalent By symmetry Sigma ( σ ) Pi ( π ) Delta ( δ ) Phi ( φ ) By multiplicity 1 ( single ) 2 ( double ) 3 ( triple ) 4 ( quadruple ) 5 ( quintuple ) 6 ( sextuple ) Miscellaneous Agostic Bent Coordinate ( dipolar ) Pi backbond Charge - shift Hapticity Conjugation Hyperconjugation Antibonding Resonant Electron deficiency 3c -- 2e 4c -- 2e Hypercoordination 3c -- 4e Aromaticity möbius super sigma homo bicyclo spiro σ - bishomo spherical Y - Metallic Metal aromaticity Ionic Intermolecular ( weak ) van der Waals forces London dispersion Hydrogen Low - barrier Resonance - assisted Symmetric Dihydrogen bonds C -- H O interaction Noncovalent other Mechanical Halogen Chalcogen Aurophilicity Intercalation Stacking Cation -- pi Anion -- pi Salt bridge Bond cleavage Heterolysis Homolysis Retrieved from `` https://en.wikipedia.org/w/index.php?title=Chemical_change&oldid=805988470 '' Categories : Chemical reactions Hidden categories : Wikipedia indefinitely semi-protected pages Articles lacking sources from September 2014 All articles lacking sources Articles needing additional references from January 2010 All articles needing additional references Articles with multiple maintenance issues Talk View source Contents About Wikipedia Català Ελληνικά Gaelg हिन्दी Kreyòl ayisyen മലയാളം नेपाली Simple English Slovenščina Türkçe 4 more Edit links This page was last edited on 18 October 2017, at 22 : 48. 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Question: list three types of evidence that indicate a chemical reaction
Answer: Change of odor