What is Reaction: Definition and 1000 Discussions

A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions 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 (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
The substance (or substances) initially involved in a chemical reaction are called reactants or reagents. Chemical reactions are usually characterized by a chemical change, and they yield one or more products, which usually have properties different from the reactants. Reactions often consist of a sequence of individual sub-steps, the so-called elementary reactions, and the information on the precise course of action is part of the reaction mechanism. Chemical reactions are described with chemical equations, which symbolically present the starting materials, end products, and sometimes intermediate products and reaction conditions.
Chemical reactions happen at a characteristic reaction rate at a given temperature and chemical concentration. Typically, reaction rates increase with increasing temperature because there is more thermal energy available to reach the activation energy necessary for breaking bonds between atoms.
Reactions may proceed in the forward or reverse direction until they go to completion or reach equilibrium. Reactions that proceed in the forward direction to approach equilibrium are often described as spontaneous, requiring no input of free energy to go forward. Non-spontaneous reactions require input of free energy to go forward (examples include charging a battery by applying an external electrical power source, or photosynthesis driven by absorption of electromagnetic radiation in the form of sunlight).
A reaction may be classified as redox in which oxidation and reduction occur or nonredox in which there is no oxidation and reduction occurring. Most simple redox reactions may be classified as combination, decomposition, or single displacement reactions.
Different chemical reactions are used during chemical synthesis in order to obtain a desired product. In biochemistry, a consecutive series of chemical reactions (where the product of one reaction is the reactant of the next reaction) form metabolic pathways. These reactions are often catalyzed by protein enzymes. Enzymes increase the rates of biochemical reactions, so that metabolic syntheses and decompositions impossible under ordinary conditions can occur at the temperatures and concentrations present within a cell.
The general concept of a chemical reaction has been extended to reactions between entities smaller than atoms, including nuclear reactions, radioactive decays, and reactions between elementary particles, as described by quantum field theory.

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  1. K

    Rate of reaction? (UV and heat)

    I remember when I was in high school, heat was very often said to be a factor of speeding up chemical reactions that we all know, because heat is actually energy, energy will excite the molecules and make them easier to collide with other molecules or leave its own molecules (breaking bond)...
  2. K

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  3. duchuy

    Chemistry Understanding the Mechanism of E1 Reaction on Levosalbutamol

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  4. Quester

    Coil Compression Spring Reaction to a Pulse

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  5. M

    Biology How Do Stoichiometric Coefficients Affect Reaction Rates?

    Hi, I was attempting the following question and don't know how to find the 'reaction rate': "For the reaction the following stoichiometric coefficients have been determined: 2 ##C## react to form 2 ##E## and 1 ##F##. The rate of formation of E is ##1.6\times10^{–4} mol L^{–1} s^{–1}##. What is...
  6. duchuy

    Chemistry Are there alternative hydrogen abstraction pathways in E2 elimination reactions?

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  7. T

    COVID Reaction to COVID-19 Vaccine (or what to be prepared for)

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  8. I

    Chemistry Rate law for reaction of NO and H2

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  9. I

    Chemistry Reaction Mechanism of Cl2 and CHCl3

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  10. I

    Chemistry What is the relationship between temperature and reaction rate?

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  11. J

    Electromagnetic inertial reaction force?

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  12. Cheesycheese213

    Electrolysis of Water -- Rate of Reaction?

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  13. R

    MATLAB Plotting Reaction Rate vs Temperature with MATLAB

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  14. D

    Chemistry Calculating Kp for Gaseous Reaction: Stuck at Finding Total Moles

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  15. duchuy

    Available energy in β+ and β- nuclear reaction

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  16. A

    Engineering Calculation of the reaction forces on a welded joint

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  17. L

    Engineering Find the reaction forces of shaft AB

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  18. Beowulf_8991

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  19. jjson775

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  20. A

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  21. jjson775

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  22. D

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  23. Olivia Lam

    What is the reaction force between the ring and the hoop?

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  24. TonyCross

    Calculating Theoretical Reaction Force of Ball Traveling in Semi-Circle

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  25. I

    Chemistry Redox Reaction when a compound is both oxidized and reduced

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  26. archaic

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  27. I

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  28. P

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  29. mcrooster

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  30. goodOrBad

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  31. Like Tony Stark

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  32. I

    Why are the Two SSA Equations the Same in a Catalytic Cycle?

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  33. Like Tony Stark

    Reaction forces on a gyroscope

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  34. neilparker62

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  35. Yokoko

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  36. AnnM

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  37. Stephen Bulking

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  38. Kiah Palmer

    Chemistry Calculate the theoretical yield percentage for this reaction

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  39. Adrian Tudini

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  40. Nexus99

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  41. Kiah Palmer

    Chemistry Mass of an element required for a chemical reaction equation

    Conversion: 9.65 kg = 9650 g Mass Al = 26.98 g/mol Molar Mass Al2O3 = (2 x 26.98) + ( 3 x 16.00) = 101.96 g/mol Mol Al2O3 = 9650 g / 101.96 g/mol = 94.65 mol Mol Al Required = 94.65 mol x 2 = 189.3 mol Mass 100% Al required = 189.3 mol x 26.98 g/mol = 5.107x103 g Mass 80% Al required =...
  42. Y

    Chemistry Question about balancing a reaction

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  43. Kiah Palmer

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  44. J

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  45. PhysicoRaj

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  46. A

    Determining the reason for a forward reaction

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  47. J

    MHB Compute the reaction in the front wheels

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  48. E

    B The Missing Mass of a reaction

    Wikipedia says this about the missing mass of a reaction: I wondered where such an expression is coming from? The invariant mass of a system ##M##, in natural units, satisfies $$M^2 = \left(\sum E \right)^2 - ||\sum \mathbf{p}||^2$$ If anything, then the "missing" mass (which they also...
  49. maistral

    Reaction kinetics + Gillespie algorithm: Propensity function?

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  50. StanG_80

    Could This Chemical Reaction Have Been Dangerous to Breathe In?

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