HTTP/1.0 200 OK Cache-Control: private, must-revalidate Content-Type: text/html; charset=UTF-8 Date: Tue, 24 Nov 2020 15:19:28 GMT Expires: -1 Pragma: no-cache 富易堂 网上娱乐

Chemical reaction

print Print
Please select which sections you would like to print:
Feedback
Corrections? Updates? Omissions? Let us know if you have suggestions to improve this article (requires login).
Thank you for your feedback

The upshot: The world's largest economy can still function as an oasis in a desert despite the claims of doomsayers that those days are over.

Join Britannica's Publishing Partner Program and our community of experts to gain a global audience for your work!
External Websites
  • 广东建材打假专项行动:混凝土用砂合格率100%
  • 福布斯华人富豪榜:李嘉诚蝉联首富 王健林进前三
Britannica Websites
Articles from Britannica Encyclopedias for elementary and high school students.
  • 江苏首例耕地资源保护案宣判

Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical elements or compounds. A chemical reaction rearranges the constituent atoms of the reactants to create different substances as products.

Top Questions

What are the basics of chemical reactions?

What happens to chemical bonds when a chemical reaction takes place?

How are chemical reactions classified?

Chemical reactions are an integral part of technology, of culture, and indeed of life itself. Burning fuels, smelting iron, making glass and pottery, brewing beer, and making wine and cheese are among many examples of activities incorporating chemical reactions that have been known and used for thousands of years. Chemical reactions abound in the geology of Earth, in the atmosphere and oceans, and in a vast array of complicated processes that occur in all living systems.

Chemical reactions must be distinguished from physical changes. Physical changes include changes of state, such as ice melting to water and water evaporating to vapour. If a physical change occurs, the physical properties of a substance will change, but its chemical identity will remain the same. No matter what its physical state, water (H2O) is the same compound, with each molecule composed of two atoms of hydrogen and one atom of oxygen. However, if water, as ice, liquid, or vapour, encounters sodium metal (Na), the atoms will be redistributed to give the new substances molecular hydrogen (H2) and sodium hydroxide (NaOH). By this, we know that a chemical change or reaction has occurred.

Historical overview

The concept of a chemical reaction dates back about 250 years. It had its origins in early experiments that classified substances as elements and compounds and in theories that explained these processes. Development of the concept of a chemical reaction had a primary role in defining the science of chemistry as it is known today.

Get exclusive access to content from our 1768 First Edition with your subscription. Subscribe today

The first substantive studies in this area were on gases. The identification of oxygen in the 18th century by Swedish chemist Carl Wilhelm Scheele and English clergyman Joseph Priestley had particular significance. The influence of French chemist Antoine-Laurent Lavoisier was especially notable, in that his insights confirmed the importance of quantitative measurements of chemical processes. In his book Traité élémentaire de chimie (1789; Elementary Treatise on Chemistry), Lavoisier identified 33 “elements”—substances not broken down into simpler entities. Among his many discoveries, Lavoisier accurately measured the weight gained when elements were oxidized, and he ascribed the result to the combining of the element with oxygen. The concept of chemical reactions involving the combination of elements clearly emerged from his writing, and his approach led others to pursue experimental chemistry as a quantitative science.

The other occurrence of historical significance concerning chemical reactions was the development of atomic theory. For this, much credit goes to English chemist John Dalton, who postulated his atomic theory early in the 19th century. Dalton maintained that matter is composed of small, indivisible particles, that the particles, or atoms, of each element were unique, and that chemical reactions were involved in rearranging atoms to form new substances. This view of chemical reactions accurately defines the current subject. Dalton’s theory provided a basis for understanding the results of earlier experimentalists, including the law of conservation of matter (matter is neither created nor destroyed) and the law of constant composition (all samples of a substance have identical elemental compositions).

一家非官方机构出具的中国制造业衡量指标在11月下降,表明国有企业的业务增长并未扩展到规模较小和私营的工厂。
人们对于可穿戴设备销量的估计各不相同。研究公司IDC认为,这类设备今年的销量将超过1,900万件量,达到去年的三倍以上。到2018年,它的销量将会达到1.119亿件。瑞士信贷(Credit Suisse)预计,在接下来的2-4年中,这个行业的价值将会高达300亿至500亿美元。不过,在这一切实现之前,这个方兴未艾的市场需要摆脱人们对于“穿戴这种设备就是出丑”的成见。
Chinese manufacturers:Coming to the U.S.? Warren Buffett’s BYD says it is arriving in 2015 and Geely in 2016 but we’ve been hearing that someone was coming since at 2006. The refinement of Chinese cars is the issue. With more than 80 local automakers producing 524 different models in China, R&D money is spread too thinly to produce meaningful results.
silicon

Basic concepts of chemical reactions

Synthesis

When making a new substance from other substances, chemists say either that they carry out a synthesis or that they synthesize the new material. Reactants are converted to products, and the process is symbolized by a chemical equation. For example, iron (Fe) and sulfur (S) combine to form iron sulfide (FeS). Fe(s) + S(s) → FeS(s) The plus sign indicates that iron reacts with sulfur. The arrow signifies that the reaction “forms” or “yields” iron sulfide, the product. The state of matter of reactants and products is designated with the symbols (s) for solids, (l) for liquids, and (g) for gases.

Our latest podcast episode features popular TED speaker Mara Mintzer.
Learn More!